Fix Intel/LLVM openmp build

Signed-off-by: Michał Górny <[email protected]>

Author: isuruf

recipe/meta.yaml

@@ -62,6 +62,7 @@ source:
       - patches/0014-skip-test_norm_matrix_degenerate_shapes-on-numpy-2.3.patch
       # backport https://github.com/pytorch/pytorch/pull/127702
       - patches/0015-Define-PY_SSIZE_T_CLEAN-before-include-Python.h.patch
+      - patches/0018-Use-Intel-LLVM-openmp.patch
       - patches_submodules/fbgemm/0001-remove-DESTINATION-lib-from-CMake-install-directives.patch     # [win]
       - patches_submodules/tensorpipe/0001-switch-away-from-find_package-CUDA.patch
 

recipe/patches/0018-Use-Intel-LLVM-openmp.patch

@@ -0,0 +1,31 @@
+From ffbdd8bb8fa38397ad6d7958a8c4ddd80ff738eb Mon Sep 17 00:00:00 2001
+From: Isuru Fernando <[email protected]>
+Date: Thu, 31 Jul 2025 12:34:30 -0500
+Subject: [PATCH] Use Intel/LLVM openmp
+
+This make MSVC use __kmp_* symbols available in both libiomp.dll
+and libiomp5md.dll instead of vcomp* symbols which are only in
+vcomp140.dll and libiomp5md.dll, but are missing in libiomp.dll
+---
+ cmake/Modules/FindOpenMP.cmake | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/cmake/Modules/FindOpenMP.cmake b/cmake/Modules/FindOpenMP.cmake
+index 8a9abff398..336a9a927a 100644
+--- a/cmake/Modules/FindOpenMP.cmake
++++ b/cmake/Modules/FindOpenMP.cmake
+@@ -122,9 +122,9 @@ function(_OPENMP_FLAG_CANDIDATES LANG)
+     set(OMP_FLAG_MIPSpro "-mp")
+     if(__header_dir MATCHES ".*Microsoft Visual Studio.*")
+       # MSVC header. No need to pass it as additional include.
+-      set(OMP_FLAG_MSVC "-openmp:experimental" "-openmp")
++      set(OMP_FLAG_MSVC "-openmp:llvm" "-openmp:experimental" "-openmp")
+     else()
+-      set(OMP_FLAG_MSVC "-openmp:experimental -I${__header_dir}" "-openmp -I${__header_dir}")
++      set(OMP_FLAG_MSVC "-openmp:llvm" "-openmp:experimental -I${__header_dir}" "-openmp -I${__header_dir}")
+     endif()
+     set(OMP_FLAG_PathScale "-openmp")
+     set(OMP_FLAG_NAG "-openmp")
+-- 
+2.45.2
+