testsuite: Add missing <exception> header to testcase

This test no longer compiles because <new> stopped including
<exception>, so std::set_terminate is not defined.

gcc/testsuite/ChangeLog:

	* g++.old-deja/g++.abi/cxa_vec.C: Include <exception> for
	std::set_terminate.

gcc/testsuite/g++.old-deja/g++.abi/cxa_vec.C

@@ -15,6 +15,7 @@
 #include <cxxabi.h>
 #include <stdio.h>
 #include <new>
+#include <exception>
 #include <stdlib.h>
 #include <setjmp.h>