build: allow any GCC version

build: allow any GCC version

The existing test didn't work on modern GCC; a clean fix didn't work
on modern macOS due to its aliasing gcc to clang; and the test being
done is for a version of GCC from 2013 that doesn't ship on any modern
Linux system. (RHEL7 is on GCC 4, but hasn't shipped the buggy version
either ever or since 2015, depending on which source material I look
at.)

Closes #2023