[cmake] Don't generate per-file "__SHORT_FILE__" defines on MSVC builds

As reported on llvm#150677 - this prevents build parallelisation as cmake is repeatedly updating the cache

Author: RKSimon

llvm/cmake/modules/LLVMProcessSources.cmake

@@ -58,14 +58,16 @@ function(llvm_process_sources OUT_VAR)
   set(sources ${ARG_UNPARSED_ARGUMENTS})
   llvm_check_source_file_list(${sources})
 
-  foreach(fn ${sources})
-    get_filename_component(suf ${fn} EXT)
-    if("${suf}" STREQUAL ".cpp" OR "${suf}" STREQUAL ".c")
-      get_filename_component(short_name ${fn} NAME)
-      set_source_files_properties(${fn} PROPERTIES COMPILE_DEFINITIONS "__SHORT_FILE__=\"${short_name}\"")
-    endif()
-  endforeach()
-
+  # Don't generate __SHORT_FILE__ on MSVC builds as it can force repeated cache regeneration.
+  if(NOT MSVC)
+    foreach(fn ${sources})
+      get_filename_component(suf ${fn} EXT)
+      if("${suf}" STREQUAL ".cpp" OR "${suf}" STREQUAL ".c")
+        get_filename_component(short_name ${fn} NAME)
+        set_source_files_properties(${fn} PROPERTIES COMPILE_DEFINITIONS "__SHORT_FILE__=\"${short_name}\"")
+      endif()
+    endforeach()
+  endif()
 
   # This adds .td and .h files to the Visual Studio solution:
   add_td_sources(sources)