Index: llvm/cmake/modules/HandleLLVMOptions.cmake
===================================================================
--- llvm/cmake/modules/HandleLLVMOptions.cmake
+++ llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -681,7 +681,7 @@
     string(REGEX REPLACE " /W[0-4]" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
 
     if (LLVM_ENABLE_PEDANTIC)
-      # No MSVC equivalent available
+      append("/permissive-" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
     endif (LLVM_ENABLE_PEDANTIC)
   endif (LLVM_ENABLE_WARNINGS)