Use ompstub by default on Windows on ARM

OpenMP is not supported on Windows on ARM yet.
Therefore this PR modified Cmakelist to use ompstub
on Windows on ARM for linking by default.

runtime/flangrti/CMakeLists.txt

@@ -81,11 +81,16 @@ endif()
 
 # Import OpenMP
 if (NOT DEFINED LIBOMP_EXPORT_DIR)
-  find_library( 
-    FLANG_LIBOMP
-    libomp.so
-    HINTS ${CMAKE_BINARY_DIR}/lib)
-  target_link_libraries(flangrti_shared ${FLANG_LIBOMP})
+  # OpenMP is not supported on Windows on ARM yet, use ompstub for linking by default
+  if(NOT (MSVC AND ${TARGET_ARCHITECTURE} STREQUAL "aarch64"))
+    find_library(
+      FLANG_LIBOMP
+      NAMES omp libomp
+      HINTS ${CMAKE_BINARY_DIR}/lib)
+    target_link_libraries(flangrti_shared PRIVATE ${FLANG_LIBOMP})
+  else()
+    target_link_libraries(flangrti_shared PRIVATE ompstub_shared)
+  endif()
 endif()
 
 find_library(