Detect ancient GCC specifically, rather than using target architecture as a
crude heuristic.
Side note: compilers should really ignore -Wno- and -Wno-error= flags they
don't recognize. Seems like modern compilers produce warnings instead of
errors. Though, with -Werror they turn into errors. Clang's error can be
disabled with -Wno-error=unknown-warning-option, but GCC doesn't seem to
have a named method to disable the specific warning.
Submitted by: rpokala@ (earlier version)
Suggested by: rpokala@
Reviewed by: tinderbox
Sponsored by: Dell EMC Isilon
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