Merge pull request #2589 from RosettaCommons/roccomoretti/older_gcc_fix
Fix OLDER_GCC define for e.g. Clang on Linux
The issue is not so much the older GCC, but the older libstdc++ which comes with older GCC versions. Testing for GCC version (like we were doing) doesn't help platforms/situations where another compiler (e.g. Clang on Linux) is using the older GCC's stdlib. This PR attempts to test the STDLIB version directly.