Revert "Blind attempt to fix _configthreadlocale() failures on MinGW."

This reverts commit 2cf91ccb73ce888c44e3751548fb7c77e87335f2.

When using the old msvcrt.dll, MinGW would supply its own dummy version
of _configthreadlocale() that just returns -1 if you try to use it.  For
a time we tolerated that to shut the build farm up.  We would fall back
to code that was enough for the tests to pass, but it would surely have
risked crashing a real multithreaded program.

We don't need that kludge anymore, because we can count on ucrt.  We
expect the real _configthreadlocale() to be present, and the ECPG tests
will now fail if it isn't.  The workaround was dead code and it's time
to revert it.

(A later patch still under review proposes to remove this use of
_configthreadlocale() completely but we're unwinding this code in
steps.)

Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/d9e7731c-ca1b-477c-9298-fa51e135574a%40eisentraut.org

src/interfaces/ecpg/ecpglib/descriptor.c

@@ -512,7 +512,7 @@ ECPGget_desc(int lineno, const char *desc_name, int index,...)
 		}
 #ifdef WIN32
 		if (stmt.oldthreadlocale != -1)
-			(void) _configthreadlocale(stmt.oldthreadlocale);
+			_configthreadlocale(stmt.oldthreadlocale);
 #endif
 #endif
 	}

src/interfaces/ecpg/ecpglib/execute.c

@@ -1977,9 +1977,7 @@ ecpg_do_prologue(int lineno, const int compat, const int force_indicator,
 	 * Make sure we do NOT honor the locale for numeric input/output since the
 	 * database wants the standard decimal point.  If available, use
 	 * uselocale() for this because it's thread-safe.  Windows doesn't have
-	 * that, but it usually does have _configthreadlocale().  In some versions
+	 * that, but it does have _configthreadlocale().
-	 * of MinGW, _configthreadlocale() exists but always returns -1 --- so
-	 * treat that situation as if the function doesn't exist.
 	 */
 #ifdef HAVE_USELOCALE
 
@@ -1997,6 +1995,11 @@ ecpg_do_prologue(int lineno, const int compat, const int force_indicator,
 #else
 #ifdef WIN32
 	stmt->oldthreadlocale = _configthreadlocale(_ENABLE_PER_THREAD_LOCALE);
+	if (stmt->oldthreadlocale == -1)
+	{
+		ecpg_do_epilogue(stmt);
+		return false;
+	}
 #endif
 	stmt->oldlocale = ecpg_strdup(setlocale(LC_NUMERIC, NULL), lineno);
 	if (stmt->oldlocale == NULL)
@@ -2218,17 +2221,12 @@ ecpg_do_epilogue(struct statement *stmt)
 		uselocale(stmt->oldlocale);
 #else
 	if (stmt->oldlocale)
+	{
 		setlocale(LC_NUMERIC, stmt->oldlocale);
 #ifdef WIN32
-
+		_configthreadlocale(stmt->oldthreadlocale);
-	/*
-	 * This is a bit trickier than it looks: if we failed partway through
-	 * statement initialization, oldthreadlocale could still be 0.  But that's
-	 * okay because a call with 0 is defined to be a no-op.
-	 */
-	if (stmt->oldthreadlocale != -1)
-		(void) _configthreadlocale(stmt->oldthreadlocale);
 #endif
+	}
 #endif
 
 	free_statement(stmt);