cmake: Better detection of Clang version, including Apple vs OSS Clang. Refactoring for simplification of the compiler-specific bits of the CMakefile.
cmake: Better detection of Clang version, including Apple vs OSS Clang.
Refactoring for simplification of the compiler-specific bits of the
CMakefile.

brechtvl/OpenShadingLanguage,aconty/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,gzorin/OpenShadingLanguage,rlmh/OpenShadingLanguage,rlmh/OpenShadingLanguage,gzorin/OpenShadingLanguage,brechtvl/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,lgritz/OpenShadingLanguage,aconty/OpenShadingLanguage,rlmh/OpenShadingLanguage,brechtvl/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,imageworks/OpenShadingLanguage,brechtvl/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,gzorin/OpenShadingLanguage,imageworks/OpenShadingLanguage,lgritz/OpenShadingLanguage,gzorin/OpenShadingLanguage,svenstaro/OpenShadingLanguage,lgritz/OpenShadingLanguage,imageworks/OpenShadingLanguage,svenstaro/OpenShadingLanguage,rlmh/OpenShadingLanguage,svenstaro/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,imageworks/OpenShadingLanguage,imageworks/OpenShadingLanguage,aconty/OpenShadingLanguage,aconty/OpenShadingLanguage,lgritz/OpenShadingLanguage,lgritz/OpenShadingLanguage,svenstaro/OpenShadingLanguage,brechtvl/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,gzorin/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,aconty/OpenShadingLanguage