diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -62,18 +62,19 @@
     # NOTE: use `add_compile_options` rather than `add_definitions` since
     # `add_definitions` does not support generator expressions.
     add_compile_options($<$<OR:$<COMPILE_LANGUAGE:C>,$<COMPILE_LANGUAGE:CXX>>:-UNDEBUG>)
-
-    # Also remove /D NDEBUG to avoid MSVC warnings about conflicting defines.
-    foreach (flags_var_to_scrub
-        CMAKE_CXX_FLAGS_RELEASE
-        CMAKE_CXX_FLAGS_RELWITHDEBINFO
-        CMAKE_CXX_FLAGS_MINSIZEREL
-        CMAKE_C_FLAGS_RELEASE
-        CMAKE_C_FLAGS_RELWITHDEBINFO
-        CMAKE_C_FLAGS_MINSIZEREL)
-      string (REGEX REPLACE "(^| )[/-]D *NDEBUG($| )" " "
-        "${flags_var_to_scrub}" "${${flags_var_to_scrub}}")
-    endforeach()
+    if (MSVC)
+      # Also remove /D NDEBUG to avoid MSVC warnings about conflicting defines.
+      foreach (flags_var_to_scrub
+          CMAKE_CXX_FLAGS_RELEASE
+          CMAKE_CXX_FLAGS_RELWITHDEBINFO
+          CMAKE_CXX_FLAGS_MINSIZEREL
+          CMAKE_C_FLAGS_RELEASE
+          CMAKE_C_FLAGS_RELWITHDEBINFO
+          CMAKE_C_FLAGS_MINSIZEREL)
+        string (REGEX REPLACE "(^| )[/-]D *NDEBUG($| )" " "
+          "${flags_var_to_scrub}" "${${flags_var_to_scrub}}")
+      endforeach()
+     endif()
   endif()
 endif()