[CMake] Fix LLVM_ENABLE_EH and LLVM_ENABLE_RTTI on MSVC

[jsroemer]

Summary

I just enabled LLVM_ENABLE_EH and LLVM_ENABLE_RTTI for all my platforms due to compatibility issues on Linux and noticed a massive number of warnings from xlocal that /EHsc should be enabled. I traced this down to HandleLLVMOptions unconditionally removing all EH and RTTI flags on MSVC (lines 609-616) and llvm_update_compile_flags not adding them back. In other words, as of right now, these options are broken on MSVC. The attached patch adds the flags back as required.

[rnk]

lgtm

It's unfortunate that we have to globally remove /EHsc and /GR in HandleLLVMOptions just to avoid warnings, but I don't think we can avoid it.

[jsroemer]

Ok, great, can you or someone else land the patch? I don't have commit rights.

Personally, I think the issue is that we have an option like LLVM_ENABLE_EH at all instead of respecting what the user sets via CMAKE_${LANG}_FLAGS, but that's a different discussion.

[rnk]

Thanks Andrey! I was sick/busy last week.

llvm/trunk/cmake/modules/AddLLVM.cmake

function(llvm_update_compile_flags name)
 
   # LLVM_REQUIRES_EH is an internal flag that individual targets can use to
   # force EH
   if(LLVM_REQUIRES_EH OR LLVM_ENABLE_EH)
     if(NOT (LLVM_REQUIRES_RTTI OR LLVM_ENABLE_RTTI))
       message(AUTHOR_WARNING "Exception handling requires RTTI. Enabling RTTI for ${name}")
       set(LLVM_REQUIRES_RTTI ON)
     endif()
+    if(MSVC)
+      list(APPEND LLVM_COMPILE_FLAGS "/EHsc")
+    endif()
   else()
     if(LLVM_COMPILER_IS_GCC_COMPATIBLE)
       list(APPEND LLVM_COMPILE_FLAGS "-fno-exceptions")
     elseif(MSVC)
       list(APPEND LLVM_COMPILE_DEFINITIONS _HAS_EXCEPTIONS=0)
       list(APPEND LLVM_COMPILE_FLAGS "/EHs-c-")
     endif()
   endif()
 
   # LLVM_REQUIRES_RTTI is an internal flag that individual
   # targets can use to force RTTI
   set(LLVM_CONFIG_HAS_RTTI YES CACHE INTERNAL "")
   if(NOT (LLVM_REQUIRES_RTTI OR LLVM_ENABLE_RTTI))
     set(LLVM_CONFIG_HAS_RTTI NO CACHE INTERNAL "")
     list(APPEND LLVM_COMPILE_DEFINITIONS GTEST_HAS_RTTI=0)
     if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
       list(APPEND LLVM_COMPILE_FLAGS "-fno-rtti")
     elseif (MSVC)
       list(APPEND LLVM_COMPILE_FLAGS "/GR-")
     endif ()
+  elseif(MSVC)
+    list(APPEND LLVM_COMPILE_FLAGS "/GR")
   endif()
 
   # Assume that;
   #   - LLVM_COMPILE_FLAGS is list.
   #   - PROPERTY COMPILE_FLAGS is string.
   string(REPLACE ";" " " target_compile_flags " ${LLVM_COMPILE_FLAGS}")
 
   if(update_src_props)