flags for GCC compilers version 4.8 and above. Removed files from gnu-warnings that only apply to versions < 4.8. Consolidated warnings from versions < 4.8 that apply to versions >= 4.8 into the 4.8 warnings files.
the filename prefixes. Update config/gnu-flags to suit. I also made changes to config/cmake/HDFCompilerFlags.cmake, but I'm not sure they're correct.