Remove configure check for _configthreadlocale().

All modern Windows systems have _configthreadlocale().  It was first
introduced in msvcr80.dll from Visual Studio 2005.  Historically, MinGW
was stuck on even older msvcrt.dll, but added its own dummy
implementation of the function when using msvcrt.dll years ago anyway,
effectively rendering the configure test useless.  In practice we don't
encounter the dummy anymore because modern MinGW uses ucrt.

Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/CWZBBRR6YA8D.8EHMDRGLCKCD%40neon.tech

configure

@@ -15821,17 +15821,6 @@ fi
 
 # Win32 (really MinGW) support
 if test "$PORTNAME" = "win32"; then
-  for ac_func in _configthreadlocale
-do :
-  ac_fn_c_check_func "$LINENO" "_configthreadlocale" "ac_cv_func__configthreadlocale"
-if test "x$ac_cv_func__configthreadlocale" = xyes; then :
-  cat >>confdefs.h <<_ACEOF
-#define HAVE__CONFIGTHREADLOCALE 1
-_ACEOF
-
-fi
-done
-
   case " $LIBOBJS " in
   *" dirmod.$ac_objext "* ) ;;
   *) LIBOBJS="$LIBOBJS dirmod.$ac_objext"

configure.ac

@@ -1820,7 +1820,6 @@ fi
 
 # Win32 (really MinGW) support
 if test "$PORTNAME" = "win32"; then
-  AC_CHECK_FUNCS(_configthreadlocale)
   AC_LIBOBJ(dirmod)
   AC_LIBOBJ(kill)
   AC_LIBOBJ(open)

meson.build

@@ -2617,7 +2617,6 @@ endif
 # XXX: Might be worth conditioning some checks on the OS, to avoid doing
 # unnecessary checks over and over, particularly on windows.
 func_checks = [
-  ['_configthreadlocale', {'skip': host_system != 'windows'}],
   ['backtrace_symbols', {'dependencies': [execinfo_dep]}],
   ['clock_gettime', {'dependencies': [rt_dep], 'define': false}],
   ['copyfile'],

src/include/pg_config.h.in

@@ -529,9 +529,6 @@
 /* Define to 1 if your compiler understands __builtin_unreachable. */
 #undef HAVE__BUILTIN_UNREACHABLE
 
-/* Define to 1 if you have the `_configthreadlocale' function. */
-#undef HAVE__CONFIGTHREADLOCALE
-
 /* Define to 1 if you have __cpuid. */
 #undef HAVE__CPUID
 

src/interfaces/ecpg/ecpglib/descriptor.c

@@ -490,7 +490,7 @@ ECPGget_desc(int lineno, const char *desc_name, int index,...)
 		Assert(ecpg_clocale);
 		stmt.oldlocale = uselocale(ecpg_clocale);
 #else
-#ifdef HAVE__CONFIGTHREADLOCALE
+#ifdef WIN32
 		stmt.oldthreadlocale = _configthreadlocale(_ENABLE_PER_THREAD_LOCALE);
 #endif
 		stmt.oldlocale = ecpg_strdup(setlocale(LC_NUMERIC, NULL), lineno);
@@ -510,7 +510,7 @@ ECPGget_desc(int lineno, const char *desc_name, int index,...)
 			setlocale(LC_NUMERIC, stmt.oldlocale);
 			ecpg_free(stmt.oldlocale);
 		}
-#ifdef HAVE__CONFIGTHREADLOCALE
+#ifdef WIN32
 		if (stmt.oldthreadlocale != -1)
 			(void) _configthreadlocale(stmt.oldthreadlocale);
 #endif

src/interfaces/ecpg/ecpglib/ecpglib_extern.h

@@ -77,7 +77,7 @@ struct statement
 	locale_t	oldlocale;
 #else
 	char	   *oldlocale;
-#ifdef HAVE__CONFIGTHREADLOCALE
+#ifdef WIN32
 	int			oldthreadlocale;
 #endif
 #endif

src/interfaces/ecpg/ecpglib/execute.c

@@ -1995,7 +1995,7 @@ ecpg_do_prologue(int lineno, const int compat, const int force_indicator,
 		return false;
 	}
 #else
-#ifdef HAVE__CONFIGTHREADLOCALE
+#ifdef WIN32
 	stmt->oldthreadlocale = _configthreadlocale(_ENABLE_PER_THREAD_LOCALE);
 #endif
 	stmt->oldlocale = ecpg_strdup(setlocale(LC_NUMERIC, NULL), lineno);
@@ -2219,7 +2219,7 @@ ecpg_do_epilogue(struct statement *stmt)
 #else
 	if (stmt->oldlocale)
 		setlocale(LC_NUMERIC, stmt->oldlocale);
-#ifdef HAVE__CONFIGTHREADLOCALE
+#ifdef WIN32
 
 	/*
 	 * This is a bit trickier than it looks: if we failed partway through