pgsql: Add missing include

Add missing include

"utils/pg_locale.h" is needed when under MSVC for wchar2char(),
introduced by commit 65707ed9afc.  Surprisingly, MSVC doesn't warn by
default about calling undeclared functions.  This will be addressed in
a separate commit.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/1142ad86-e475-41b3-aeee-c6ad913064fa%40eisentraut.org

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/c86d2ccdb35544590531f5431606db46b57730a8

Modified Files
--------------
src/backend/utils/error/elog.c | 1 +
1 file changed, 1 insertion(+)