[cmake] Fix LLVM_USE_SPLIT_DWARF

Summary:
- Add `-gsplit-dwarf` as an option instead of a definition.
- Only add that option on compilers supporting dwarf splitting, such as clang
  and gcc.

Reviewers: echristo, pcc

Subscribers: mgorny, aprantl, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D75328

Author: darkbuck

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -746,9 +746,15 @@ if(LLVM_USE_SANITIZER)
   endif()
 endif()
 
-# Turn on -gsplit-dwarf if requested
-if(LLVM_USE_SPLIT_DWARF)
-  add_definitions("-gsplit-dwarf")
+# Turn on -gsplit-dwarf if requested in debug builds.
+if (LLVM_USE_SPLIT_DWARF AND
+    ((uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG") OR
+     (uppercase_CMAKE_BUILD_TYPE STREQUAL "RELWITHDEBINFO")))
+  # Limit to clang and gcc so far. Add compilers supporting this option.
+  if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR
+      CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+    add_compile_options(-gsplit-dwarf)
+  endif()
 endif()
 
 add_definitions( -D__STDC_CONSTANT_MACROS )