C99 comments have been the default in compilers for something like 20 years
now. This means we don't need to remember to turn it on when porting software,
and gets rid of cryptic errors about unterminated character constants when
someone writes something like:
// Didn't need to...
We still accept the flag to avoid breaking mkfiles, but we do nothing with it.
This also removes the documentation, since the option does nothing now.
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