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.
g++ (older than gcc/g++ 4.2).
Correct gnu-cxxflags to determine warnings flags to be added based on
C++ compiler version instead of C compiler version.