[PATCH 9/6] git-compat-util: guard definition of MAYBE_UNUSED with __GNUC__

Just like we only define UNUSED macro when __GNUC__ is defined, and fall back to an empty definition otherwise, we should do the same for MAYBE_UNUSED.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 * Before I forget that we have discussed this, just as a
   documentation (read: this is not a patch to be applied).

   I think this only matters when a compiler satisfies all three
   traits:

   - does not define __GNUC__
   - does have its own __attribute__() macro
   - barfs on __attribute__((__unused__))

   Otherwise we will define __attribute__(x) away to empty to cause
   no harm.

   Since we have survived without complaints without such a guard
   for quite some time, it may be a sign that no compiler that knows
   __attribute__() that people ever tried to compile Git with barfs
   with __attribute__((__unused__)).  I dunno.

 git-compat-util.h | 4 ++++
 1 file changed, 4 insertions(+)