pgsql: Use thread-safe nl_langinfo_l(), not nl_langinfo().

Use thread-safe nl_langinfo_l(), not nl_langinfo().

This gets rid of some setlocale() calls. The remaining call to
setlocale() in pg_get_encoding_from_locale() is a query of the name
of the current locale when none was provided (in a multi-threaded future
that would need more work).

All known non-Windows targets have nl_langinfo_l(), from POSIX 2008, and
for Windows we already do something thread-safe.

Reviewed-by: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Discussion: https://postgr.es/m/CA%2BhUKGJqVe0%2BPv9dvC9dSums_PXxGo9SWcxYAMBguWJUGbWz-A%40mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/35eeea62302260ec07fd11b287e488768d4543e2

Modified Files
--------------
src/port/chklocale.c | 67 +++++++++++++++-------------------------------------
1 file changed, 19 insertions(+), 48 deletions(-)