Merge pull request #2592 in HDFFV/hdf5 from ~LRKNOX/hdf5_lrk:develop to develop
* commit 'fcd87d2569ca4d8396c7db4eddb46cab04010abf':
Revise gnu-*flags and cmake/HDF*CompilerFlags.cmake files to add warning 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.