Undefine setlocale() macro on Win32

New versions of libintl redefine setlocale() to a macro
which causes problems when the backend and libintl are
linked against different versions of the runtime, which
is often the case in msvc builds.

Hiroshi Inoue, slightly updated comment by me

src/include/port.h

@@ -176,6 +176,15 @@ extern unsigned char pg_tolower(unsigned char ch);
 #ifdef printf
 #undef printf
 #endif
+/*
+ * Versions of libintl >= 0.18? try to replace setlocale() with a macro
+ * to their own versions.  Remove the macro, if it exists, because it
+ * ends up calling the wrong version when the backend and libintl use
+ * different versions of msvcrt.
+ */
+#if defined(setlocale) && defined(WIN32)
+#undef setlocale
+#endif
 
 extern int	pg_vsnprintf(char *str, size_t count, const char *fmt, va_list args);
 extern int