Enable the clang build and disable gcc on osx
Enable the clang build and disable gcc on osx

As gcc just refuses to link to libc++ on osx and as most users are using
the default clang compiler on OSX, it was decided to use that instead of
gcc.

UnrealQuester/color_coded,UnrealQuester/color_coded,jeaye/color_coded,jeaye/color_coded,jeaye/color_coded,jeaye/color_coded,UnrealQuester/color_coded,UnrealQuester/color_coded