Avoid setting _LIBCPP_HAS_CATOPEN in libcxx. NFC. (#13741)

This is to avoid unnecessary calls to the message catalog functions,
which are currently not supported within Emscripten.

Note that since musl v1.1.24 these functions are supported, but this
would then add a dependency on `__map_file` (which is currently no-op).

Author: kleisauke

system/lib/libcxx/include/__config

@@ -909,7 +909,7 @@ typedef unsigned int   char32_t;
 
 #if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
 // Most unix variants have catopen.  These are the specific ones that don't.
-#  if !defined(__BIONIC__) && !defined(_NEWLIB_VERSION)
+#  if !defined(__BIONIC__) && !defined(_NEWLIB_VERSION) && !defined(__EMSCRIPTEN__) // XXX Emscripten catopen always returns -1
 #    define _LIBCPP_HAS_CATOPEN 1
 #  endif
 #endif