Build Deps: Fix ISPVC and OIDN compilation on fresh Windows

Make them to use self-compiled Python, similar to previous fixes
for other libraries.

build_files/build_environment/cmake/ispc.cmake

@@ -43,6 +43,7 @@ set(ISPC_EXTRA_ARGS
     -DISPC_INCLUDE_TESTS=Off
     -DCLANG_LIBRARY_DIR=${LIBDIR}/llvm/lib
     -DCLANG_INCLUDE_DIRS=${LIBDIR}/llvm/include
+    -DPython3_EXECUTABLE=${PYTHON_BINARY}
     ${ISPC_EXTRA_ARGS_WIN}
     ${ISPC_EXTRA_ARGS_APPLE}
     ${ISPC_EXTRA_ARGS_UNIX}
@@ -61,6 +62,7 @@ ExternalProject_Add(external_ispc
 add_dependencies(
   external_ispc
   ll
+  external_python
 )
 
 if(WIN32)

build_files/build_environment/cmake/openimagedenoise.cmake

@@ -9,6 +9,7 @@ set(OIDN_EXTRA_ARGS
   -DOIDN_STATIC_RUNTIME=OFF
   -DISPC_EXECUTABLE=${LIBDIR}/ispc/bin/ispc
   -DOIDN_FILTER_RTLIGHTMAP=OFF
+  -DPYTHON_EXECUTABLE=${PYTHON_BINARY}
 )
 
 if(WIN32)
@@ -38,6 +39,7 @@ add_dependencies(
   external_openimagedenoise
   external_tbb
   external_ispc
+  external_python
 )
 
 if(WIN32)