pgsql: Detect setlocale(LC_CTYPE, NULL) clobbering previous return valu

Detect setlocale(LC_CTYPE, NULL) clobbering previous return values.

POSIX permits setlocale() calls to invalidate any previous setlocale()
return values.  Commit 5f538ad004aa00cf0881f179f0cde789aad4f47e
neglected to account for that.  In advance of fixing that bug, switch to
failing hard on affected configurations.  This is a planned temporary
commit to assay buildfarm-represented configurations.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/b76e76be460a240e99c33f6fb470dd1d5fe01a2a

Modified Files
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src/backend/utils/adt/pg_locale.c |   14 ++++++++++++++
1 file changed, 14 insertions(+)