Remove checks for no longer supported GCC versions
Since commit
f5e0186f865 (Raise C requirement to C11), we effectively
require at least GCC version 4.7, so checks for older versions can be
removed.
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/
a0f817ee-fb86-483a-8a14-
b6f7f5991b6e%40eisentraut.org