pgsql: Select appropriate PG_PRINTF_ATTRIBUTE for recent NetBSD.

Select appropriate PG_PRINTF_ATTRIBUTE for recent NetBSD.

NetBSD-current generates a large number of warnings about "%m" not
being appropriate to use with *printf functions. While that's true
for their native printf, it's surely not true for snprintf.c, so I
think they have misunderstood gcc's definition of the "gnu_printf"
archetype. Nonetheless, choosing "__syslog__" instead silences the
warnings; so teach configure about that.

Since this is only a cosmetic warning issue (and anyway it depends
on previous hacking to be self-consistent), no back-patch.

Discussion: https://postgr.es/m/16785.1539046036@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/aed9fa0bd8973fd967724003e641a5b7054d6a80

Modified Files
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config/c-compiler.m4 | 35 +++++++++++++++++++++++++----------
configure | 41 +++++++++++++++++++++++++++++++++++------
src/include/pg_config.h.in | 2 +-
3 files changed, 61 insertions(+), 17 deletions(-)