diff --git a/CMakeLists.txt b/CMakeLists.txt
index ab7f932a128..7f41d455fa4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1559,8 +1559,10 @@ if(WITH_OPENMP)
     if(NOT WITH_OPENMP_STATIC)
       string(APPEND CMAKE_C_FLAGS " ${OpenMP_C_FLAGS}")
       string(APPEND CMAKE_CXX_FLAGS " ${OpenMP_CXX_FLAGS}")
-      string(APPEND CMAKE_EXE_LINKER_FLAGS " ${OpenMP_LINKER_FLAGS}")
-      string(APPEND CMAKE_MODULE_LINKER_FLAGS " ${OpenMP_LINKER_FLAGS}")
+      if(DEFINED OpenMP_LINKER_FLAGS)
+        string(APPEND CMAKE_EXE_LINKER_FLAGS " ${OpenMP_LINKER_FLAGS}")
+        string(APPEND CMAKE_MODULE_LINKER_FLAGS " ${OpenMP_LINKER_FLAGS}")
+      endif()
     else()
       # Typically avoid adding flags as defines but we can't
       # pass OpenMP flags to the linker for static builds, meaning
diff --git a/build_files/cmake/Modules/FindHIP.cmake b/build_files/cmake/Modules/FindHIP.cmake
index 1f93b211573..a3b7ee56f2c 100644
--- a/build_files/cmake/Modules/FindHIP.cmake
+++ b/build_files/cmake/Modules/FindHIP.cmake
@@ -7,16 +7,18 @@
 #  HIP_VERSION, the HIP compiler version
 #  HIP_FOUND, if the HIP toolkit is found.
 
+if(NOT (DEFINED HIP_ROOT_DIR))
+  set(HIP_ROOT_DIR "")
+endif()
+
 # If `HIP_ROOT_DIR` was defined in the environment, use it.
-if(DEFINED HIP_ROOT_DIR AND HIP_ROOT_DIR)
+if(HIP_ROOT_DIR)
   # Pass.
 elseif(DEFINED ENV{HIP_ROOT_DIR})
   set(HIP_ROOT_DIR $ENV{HIP_ROOT_DIR})
 elseif(DEFINED ENV{HIP_PATH})
   # Built-in environment variable from SDK.
   set(HIP_ROOT_DIR $ENV{HIP_PATH})
-else()
-  set(HIP_ROOT_DIR "")
 endif()
 
 set(_hip_SEARCH_DIRS
diff --git a/build_files/cmake/Modules/FindHIPRT.cmake b/build_files/cmake/Modules/FindHIPRT.cmake
index 60f97203f5e..600f695d110 100644
--- a/build_files/cmake/Modules/FindHIPRT.cmake
+++ b/build_files/cmake/Modules/FindHIPRT.cmake
@@ -7,16 +7,18 @@
 #   HIPRT_BITCODE, bitcode file with ray-tracing functionality
 #   HIPRT_FOUND, if SDK found
 
+if(NOT (DEFINED HIPRT_ROOT_DIR))
+  set(HIPRT_ROOT_DIR "")
+endif()
+
 # If `HIPRT_ROOT_DIR` was defined in the environment, use it.
-if(DEFINED HIPRT_ROOT_DIR AND HIPRT_ROOT_DIR)
+if(HIPRT_ROOT_DIR)
   # Pass.
 elseif(DEFINED ENV{HIPRT_ROOT_DIR})
   set(HIPRT_ROOT_DIR $ENV{HIPRT_ROOT_DIR})
 elseif(DEFINED ENV{HIP_PATH})
   # Built-in environment variable from SDK.
   set(HIPRT_ROOT_DIR $ENV{HIP_PATH})
-else()
-  set(HIPRT_ROOT_DIR "")
 endif()
 
 set(_hiprt_SEARCH_DIRS
diff --git a/build_files/cmake/Modules/FindOptiX.cmake b/build_files/cmake/Modules/FindOptiX.cmake
index 97e1c18e242..40a59099cc9 100644
--- a/build_files/cmake/Modules/FindOptiX.cmake
+++ b/build_files/cmake/Modules/FindOptiX.cmake
@@ -11,13 +11,15 @@
 #                     This can also be an environment variable.
 #  OPTIX_FOUND, If false, do not try to use OptiX.
 
+if(NOT (DEFINED OPTIX_ROOT_DIR))
+  set(OPTIX_ROOT_DIR "")
+endif()
+
 # If `OPTIX_ROOT_DIR` was defined in the environment, use it.
-if(DEFINED OPTIX_ROOT_DIR AND OPTIX_ROOT_DIR)
+if(OPTIX_ROOT_DIR)
   # Pass.
 elseif(DEFINED ENV{OPTIX_ROOT_DIR})
   set(OPTIX_ROOT_DIR $ENV{OPTIX_ROOT_DIR})
-else()
-  set(OPTIX_ROOT_DIR "")
 endif()
 
 set(_optix_SEARCH_DIRS
diff --git a/build_files/cmake/Modules/FindSYCL.cmake b/build_files/cmake/Modules/FindSYCL.cmake
index 8911aab1140..806bdebfdf9 100644
--- a/build_files/cmake/Modules/FindSYCL.cmake
+++ b/build_files/cmake/Modules/FindSYCL.cmake
@@ -12,12 +12,14 @@
 #                 This can also be an environment variable.
 #  SYCL_FOUND, If false, then don't try to use SYCL.
 
-if(DEFINED SYCL_ROOT_DIR AND SYCL_ROOT_DIR)
+if(NOT (DEFINED SYCL_ROOT_DIR))
+  set(SYCL_ROOT_DIR "")
+endif()
+
+if(SYCL_ROOT_DIR)
   # Pass.
 elseif(DEFINED ENV{SYCL_ROOT_DIR} AND NOT $ENV{SYCL_ROOT_DIR} STREQUAL "")
   set(SYCL_ROOT_DIR $ENV{SYCL_ROOT_DIR})
-else()
-  set(SYCL_ROOT_DIR "")
 endif()
 
 set(_sycl_search_dirs
diff --git a/build_files/cmake/platform/platform_unix.cmake b/build_files/cmake/platform/platform_unix.cmake
index 199e671a1fd..b8fd4589295 100644
--- a/build_files/cmake/platform/platform_unix.cmake
+++ b/build_files/cmake/platform/platform_unix.cmake
@@ -37,19 +37,21 @@ else()
     unset(LIBDIR_GLIBC228_ABI)
   endif()
 
-  if(NOT (EXISTS ${LIBDIR}))
-    if(WITH_STRICT_BUILD_OPTIONS)
-      message(SEND_ERROR
-        "Unable to find LIBDIR: ${LIBDIR}. "
-        "WITH_LIBS_PRECOMPILED needs to be able to find the LIBDIR for the precompiled libraries."
-      )
-    else()
-      message(STATUS
-        "Unable to find LIBDIR: ${LIBDIR}. system libraries may be used "
-        "(disable WITH_LIBS_PRECOMPILED to suppress this message)."
-      )
+  if(DEFINED LIBDIR)
+    if(NOT (EXISTS ${LIBDIR}))
+      if(WITH_STRICT_BUILD_OPTIONS)
+        message(SEND_ERROR
+          "Unable to find LIBDIR: ${LIBDIR}. "
+          "WITH_LIBS_PRECOMPILED needs to be able to find the LIBDIR for the precompiled libraries."
+        )
+      else()
+        message(STATUS
+          "Unable to find LIBDIR: ${LIBDIR}. system libraries may be used "
+          "(disable WITH_LIBS_PRECOMPILED to suppress this message)."
+        )
+      endif()
+      unset(LIBDIR)
     endif()
-    unset(LIBDIR)
     set(WITH_LIBS_PRECOMPILED OFF)
   endif()
 endif()
@@ -136,7 +138,11 @@ if(DEFINED tiff_DIR)
 endif()
 
 if(WITH_VULKAN_BACKEND)
-  if((DEFINED LIBDIR) AND (EXISTS "${LIBDIR}/vulkan") AND (EXISTS "${LIBDIR}/shaderc"))
+  if(DEFINED LIBDIR)
+    # If these are missing, something went wrong (outdated LIBDIR?).
+    if(NOT ((EXISTS "${LIBDIR}/vulkan") AND (EXISTS "${LIBDIR}/shaderc")))
+      message(FATAL_ERROR "${LIBDIR}/vulkan & ${LIBDIR}/shaderc are missing!")
+    endif()
     if(NOT DEFINED VULKAN_ROOT_DIR)
       set(VULKAN_ROOT_DIR ${LIBDIR}/vulkan)
     endif()
@@ -361,9 +367,11 @@ if(WITH_INPUT_NDOF)
 endif()
 
 if(WITH_CYCLES AND WITH_CYCLES_OSL)
-  set(CYCLES_OSL ${LIBDIR}/osl CACHE PATH "Path to OpenShadingLanguage installation")
-  if(EXISTS ${CYCLES_OSL} AND NOT OSL_ROOT)
-    set(OSL_ROOT ${CYCLES_OSL})
+  if(DEFINED LIBDIR)
+    set(CYCLES_OSL ${LIBDIR}/osl CACHE PATH "Path to OpenShadingLanguage installation")
+    if(EXISTS ${CYCLES_OSL} AND NOT OSL_ROOT)
+      set(OSL_ROOT ${CYCLES_OSL})
+    endif()
   endif()
   find_package_wrapper(OSL)
   set_and_warn_library_found("OSL" OSL_FOUND WITH_CYCLES_OSL)
@@ -382,7 +390,7 @@ if(WITH_CYCLES AND WITH_CYCLES_OSL)
 endif()
 add_bundled_libraries(osl/lib)
 
-if(WITH_CYCLES AND WITH_CYCLES_DEVICE_ONEAPI)
+if(WITH_CYCLES AND WITH_CYCLES_DEVICE_ONEAPI AND DEFINED LIBDIR)
   set(CYCLES_LEVEL_ZERO ${LIBDIR}/level-zero CACHE PATH "Path to Level Zero installation")
   mark_as_advanced(CYCLES_LEVEL_ZERO)
   if(EXISTS ${CYCLES_LEVEL_ZERO} AND NOT LEVEL_ZERO_ROOT_DIR)
@@ -509,7 +517,9 @@ if(WITH_PUGIXML)
 endif()
 
 if(WITH_IMAGE_WEBP)
-  set(WEBP_ROOT_DIR ${LIBDIR}/webp)
+  if(DEFINED LIBDIR)
+    set(WEBP_ROOT_DIR ${LIBDIR}/webp)
+  endif()
   find_package_wrapper(WebP)
   set_and_warn_library_found("WebP" WEBP_FOUND WITH_IMAGE_WEBP)
 endif()
@@ -712,10 +722,11 @@ if(WITH_GHOST_WAYLAND)
   # When dynamically linked WAYLAND is used and `${LIBDIR}/wayland` is present,
   # there is no need to search for the libraries as they are not needed for building.
   # Only the headers are needed which can reference the known paths.
-  if((DEFINED LIBDIR) AND (EXISTS "${LIBDIR}/wayland" AND WITH_GHOST_WAYLAND_DYNLOAD))
-    set(_use_system_wayland OFF)
-  else()
-    set(_use_system_wayland ON)
+  set(_use_system_wayland ON)
+  if(DEFINED LIBDIR)
+    if(EXISTS "${LIBDIR}/wayland" AND WITH_GHOST_WAYLAND_DYNLOAD)
+      set(_use_system_wayland OFF)
+    endif()
   endif()
 
   if(_use_system_wayland)
@@ -784,8 +795,11 @@ if(WITH_GHOST_WAYLAND)
       add_definitions(-DWITH_GHOST_WAYLAND_LIBDECOR)
     endif()
 
-    if((DEFINED LIBDIR) AND (EXISTS "${LIBDIR}/wayland/bin/wayland-scanner"))
+    if(DEFINED LIBDIR)
       set(WAYLAND_SCANNER "${LIBDIR}/wayland/bin/wayland-scanner")
+      if(NOT (EXISTS "${WAYLAND_SCANNER}"))
+        message(FATAL_ERROR "${WAYLAND_SCANNER} is missing!")
+      endif()
     else()
       pkg_get_variable(WAYLAND_SCANNER wayland-scanner wayland_scanner)
     endif()
@@ -1124,4 +1138,8 @@ if(PLATFORM_BUNDLED_LIBRARIES)
   set(PLATFORM_ENV_BUILD "LD_LIBRARY_PATH=\"${_library_paths}:$LD_LIBRARY_PATH\"")
   set(PLATFORM_ENV_INSTALL "LD_LIBRARY_PATH=${CMAKE_INSTALL_PREFIX_WITH_CONFIG}/lib/;$LD_LIBRARY_PATH")
   unset(_library_paths)
+else()
+  # Quiet unused variable warnings, unfortunately this can't be empty.
+  set(PLATFORM_ENV_BUILD "_DUMMY_ENV_VAR_=1")
+  set(PLATFORM_ENV_INSTALL "_DUMMY_ENV_VAR_=1")
 endif()
diff --git a/source/blender/io/usd/CMakeLists.txt b/source/blender/io/usd/CMakeLists.txt
index 28bf3deb25c..26c77b19c55 100644
--- a/source/blender/io/usd/CMakeLists.txt
+++ b/source/blender/io/usd/CMakeLists.txt
@@ -19,7 +19,7 @@ add_definitions(-DBOOST_ALL_NO_LIB)
 # Clang as well works around the issue.
 if(UNIX AND NOT APPLE)
   if(CMAKE_C_COMPILER_ID MATCHES "Clang")
-    if(EXISTS ${LIBDIR})
+    if(DEFINED LIBDIR)
       add_definitions(-DARCH_HAS_GNU_STL_EXTENSIONS)
     endif()
   endif()
diff --git a/source/blender/render/hydra/CMakeLists.txt b/source/blender/render/hydra/CMakeLists.txt
index ed9f3f3b027..9b1622f19ad 100644
--- a/source/blender/render/hydra/CMakeLists.txt
+++ b/source/blender/render/hydra/CMakeLists.txt
@@ -19,7 +19,7 @@ add_definitions(-DBOOST_ALL_NO_LIB)
 # Clang as well works around the issue.
 if(UNIX AND NOT APPLE)
   if(CMAKE_C_COMPILER_ID MATCHES "Clang")
-    if(EXISTS ${LIBDIR})
+    if(DEFINED LIBDIR)
       add_definitions(-DARCH_HAS_GNU_STL_EXTENSIONS)
     endif()
   endif()
diff --git a/source/creator/CMakeLists.txt b/source/creator/CMakeLists.txt
index 3242e2e00d3..13ed1176b00 100644
--- a/source/creator/CMakeLists.txt
+++ b/source/creator/CMakeLists.txt
@@ -906,8 +906,10 @@ file(REMOVE ${CMAKE_BINARY_DIR}/bin/lib/libglapi.so.0.0.0)\n
         # Install to the same directory as the source, so debian-like
         # distros are happy with their policy.
         set(_suffix "site-packages")
-        if(${PYTHON_USD_PATH} MATCHES "dist-packages")
-          set(_suffix "dist-packages")
+        if(0) # TODO: `PYTHON_USD_PATH` isn't defined anywhere.
+          if(${PYTHON_USD_PATH} MATCHES "dist-packages")
+            set(_suffix "dist-packages")
+          endif()
         endif()
         install(
           DIRECTORY ${USD_LIBRARY_DIR}/python/