Merging in latest from upstream (HDFFV/hdf5:refs/heads/develop)
* commit 'e916acd018d5a307e7690a7978a1b73e83508f2b':
Move the GNU warnings configuration under config/gnu-warnings/ and trim the filename prefixes. Update config/gnu-flags to suit.
By default, demote warnings promoted to errors back to warnings.
Incorporate the H5_ECFLAGS into the library CFLAGS. Now a bunch of errors will occur. Next commit will demote the warnings promoted to errors back to warnings again.
Break out warnings into more files that autoconf and CMake can share. This change temporarily disables the warnings that were promoted to errors, but I will add those warnings back as warnings, not errors, in the next commit.
