Meta: Enable -Wexpansion-to-defined warning for Clang

The Clang implementation of this warning protects against some undefined
pre-processor behavior while ignoring function-like macros. The gcc
implementation also warns on function-like macros, and is therefore
noisy.

CMakeLists.txt

@@ -164,7 +164,6 @@ add_compile_options(-Wno-address-of-packed-member)
 add_compile_options(-Wcast-qual)
 add_compile_options(-Wdeprecated-copy)
 add_compile_options(-Wduplicated-cond)
-add_compile_options(-Wno-expansion-to-defined)
 add_compile_options(-Wformat=2)
 add_compile_options(-Wimplicit-fallthrough)
 add_compile_options(-Wlogical-op)
@@ -191,6 +190,8 @@ add_compile_options(-g1)
 if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
  add_compile_options(-Wno-literal-suffix)
  add_compile_options(-Wno-maybe-uninitialized)
+ # Only ignore expansion-to-defined for g++, clang's implementation doesn't complain about function-like macros
+ add_compile_options(-Wno-expansion-to-defined)
  add_compile_options(-Wcast-align)
  add_compile_options(-Wdouble-promotion)
 elseif (CMAKE_CXX_COMPILER_ID MATCHES "Clang$")