NAME_MAX is defined in limits.h.

And indeed it is there on Mingw, but guarded by the Windows-specific
non-standard macro _POSIX_.

I found this suggestion that Windows system headers have not used _POSIX_
since MSVC 2013:
https://sourceforge.net/p/mingw-w64/mailman/message/33014416/

However, the macro is still used in the fixed system header with GCC 10 in
my bang-up-to-date Mingw installation.

I can't see this macro referenced anywhere in gnulib's history.

So my question is: is there something gnulib can/should do here?

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