pgsql: Second try at fixing ecpglib thread-safety problem.

Second try at fixing ecpglib thread-safety problem.

While Windows (allegedly) has _configthreadlocale() pretty far back,
it seems MinGW didn't acquire support for that till more recently.
Fortunately, we can use an autoconf probe on that toolchain,
instead of guessing whether it's there.  (Hm, I wonder whether Cygwin
will need this also.)

Per buildfarm.

Discussion: https://postgr.es/m/20190121193512.tdmcnic2yjxlufaw@alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ee27584c4a40620fb26d1729e9cc449d54d62b07

Modified Files
--------------
configure                                    | 11 +++++++++++
configure.in                                 |  1 +
src/include/pg_config.h.in                   |  3 +++
src/include/pg_config.h.win32                |  3 +++
src/interfaces/ecpg/ecpglib/descriptor.c     |  4 ++--
src/interfaces/ecpg/ecpglib/ecpglib_extern.h |  2 +-
src/interfaces/ecpg/ecpglib/execute.c        |  6 +++---
7 files changed, 24 insertions(+), 6 deletions(-)