pgsql: Blind attempt to fix _configthreadlocale() failures on MinGW.

Blind attempt to fix _configthreadlocale() failures on MinGW.

Apparently, some builds of MinGW contain a version of
_configthreadlocale() that always returns -1, indicating failure.
Rather than treating that as a curl-up-and-die condition, soldier on
as though the function didn't exist.  This leaves us without thread
safety on such MinGW versions, but we didn't have it anyway.

Discussion: https://postgr.es/m/d06a16bc-52d6-9f0d-2379-21242d7dbe81@2ndQuadrant.com

Branch
------
REL_11_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/b620cf2d47625280e631127ae7202e798257647d

Modified Files
--------------
src/interfaces/ecpg/ecpglib/descriptor.c |  2 +-
src/interfaces/ecpg/ecpglib/execute.c    | 20 +++++++++++---------
2 files changed, 12 insertions(+), 10 deletions(-)