testsuite: 32 bit AIX 2 byte wchar

32 bit AIX supports 2 byte wchar.  The wchar-multi1.C testcase assumes
4 byte wchar.  Update the testcase to require 4 byte wchar.

gcc/testsuite/ChangeLog:
	* g++.dg/cpp23/wchar-multi1.C: Require 4 byte wchar_t.

Signed-off-by: David Edelsohn <dje.gcc@gmail.com>

gcc/testsuite/g++.dg/cpp23/wchar-multi1.C

@@ -1,6 +1,7 @@
 // P2362R3 - Remove non-encodable wide character literals and multicharacter
 // wide character literals.
 // { dg-do compile }
+// { dg-require-effective-target 4byte_wchar_t }
 
 char a = 'a';
 int b = 'ab';			// { dg-warning "multi-character character constant" }