Creator: Ensure OpenMP runtime is initialized as soon as possible

This is to make sure duplicate libomp/libiomp5 runtime conflicts are
detected as soon as a second runtime is initialized. Otherwise, it may
not crash until Blender's OpenMP runtime is initialized by a feature
that uses it, making such issues possibly go unnoticed. Such a conflict
can happen when an add-on has a native module that uses OpenMP and links
to a different libomp runtime, as was the case in #125255.

Currently Blender only ships with libomp on MacOS.

---
When libomp detects such an issue it should abort and print the following message:
```
OMP: Error #15: Initializing libomp.a, but found libomp.dylib already initialized.
OMP: Hint This means that multiple copies of the OpenMP runtime have been linked into the program. That is dangerous, since it can degrade performance or cause incorrect results. The best thing to do is to ensure that only a single OpenMP runtime is linked into the process, e.g. by avoiding static linking of the OpenMP runtime in any library. As an unsafe, unsupported, undocumented workaround you can set the environment variable KMP_DUPLICATE_LIB_OK=TRUE to allow the program to continue to execute, but that may cause crashes or silently produce incorrect results. For more information, please see http://openmp.llvm.org/
```

Pull Request: https://projects.blender.org/blender/blender/pulls/130407

source/creator/CMakeLists.txt

@@ -40,6 +40,12 @@ if(WITH_TBB)
   list(INSERT LIB 0 bf_blenkernel)
 endif()
 
+if(WITH_OPENMP AND WITH_OPENMP_STATIC)
+  list(APPEND LIB
+    ${OpenMP_LIBRARIES}
+  )
+endif()
+
 if(WIN32)
   list(APPEND INC ../../intern/utfconv)
 endif()

source/creator/creator.cc

@@ -82,6 +82,10 @@
 #  include <floatingpoint.h>
 #endif
 
+#ifdef _OPENMP
+#  include <omp.h>
+#endif
+
 #ifdef WITH_BINRELOC
 #  include "binreloc.h"
 #endif
@@ -300,12 +304,19 @@ int main(int argc,
   setvbuf(stdout, nullptr, _IONBF, 0);
 #endif
 
-#ifdef WIN32
-/* We delay loading of OPENMP so we can set the policy here. */
-#  if defined(_MSC_VER)
+#ifdef _OPENMP
+#  if defined(WIN32) && defined(_MSC_VER)
+  /* We delay loading of OPENMP so we can set the policy here. */
   _putenv_s("OMP_WAIT_POLICY", "PASSIVE");
 #  endif
+  /* Ensure the OpenMP runtime is initialized as soon as possible to make sure duplicate
+   * libomp/libiomp5 runtime conflicts are detected as soon as a second runtime is initialized.
+   * Initialization must be done after setting any relevant environment variables, but before
+   * installing signal handlers. */
+  omp_get_max_threads();
+#endif
 
+#ifdef WIN32
 #  ifdef USE_WIN32_UNICODE_ARGS
   /* Win32 Unicode Arguments. */
   {