Fix MinGW build, broken by my previous patch to add a setlocale() wrapper

on Windows. ecpglib doesn't link with libpgport, but picks and compiles
the .c files it needs individually. To cope with that, move the setlocale()
wrapper from chklocale.c to a separate setlocale.c file, and include that
in ecpglib.

src/tools/msvc/Mkvcbuild.pm

@@ -53,7 +53,7 @@ sub mkvcbuild
       snprintf.c strlcat.c strlcpy.c dirmod.c exec.c noblock.c path.c
       pgcheckdir.c pgmkdirp.c pgsleep.c pgstrcasecmp.c qsort.c qsort_arg.c
       sprompt.c thread.c getopt.c getopt_long.c dirent.c rint.c win32env.c
-      win32error.c);
+      win32error.c win32setlocale.c);
 
     $libpgport = $solution->AddProject('libpgport','lib','misc');
     $libpgport->AddDefine('FRONTEND');