[CMake] Add mapping for IBM XL -qnoeh and -qnortti

[hubert.reinterpretcast]

Summary

This patch maps in the -qnoeh and -qnortti options for building with IBM XL compilers.

[hubert.reinterpretcast]

Remove accidentally added empty directories.

[daltenty]

LGTM

cmake/modules/AddLLVM.cmake

if(LLVM_COMPILER_IS_GCC_COMPATIBLE)
       list(APPEND LLVM_COMPILE_FLAGS "-fno-exceptions")
       if(NOT LLVM_ENABLE_UNWIND_TABLES)
         list(APPEND LLVM_COMPILE_FLAGS "-fno-unwind-tables")
         list(APPEND LLVM_COMPILE_FLAGS "-fno-asynchronous-unwind-tables")
       endif()
     elseif(MSVC)
       list(APPEND LLVM_COMPILE_DEFINITIONS _HAS_EXCEPTIONS=0)
       list(APPEND LLVM_COMPILE_FLAGS "/EHs-c-")
+    elseif (CMAKE_CXX_COMPILER_ID MATCHES "XL")
+      list(APPEND LLVM_COMPILE_FLAGS "-qnoeh")
     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-")
+    elseif (CMAKE_CXX_COMPILER_ID MATCHES "XL")
+      list(APPEND LLVM_COMPILE_FLAGS "-qnortti")
     endif ()
   elseif(MSVC)
     list(APPEND LLVM_COMPILE_FLAGS "/GR")
   endif()
 
   # Assume that;
   #   - LLVM_COMPILE_FLAGS is list.
   #   - PROPERTY COMPILE_FLAGS is string.