libstdc++: Fix test failure on AIX

This fixes a test failure due to a non-reserved name in an AIX system
header (included via <pthread.h>). That name clashes with one of the
names we check our own headers for, so skip checking that name on AIX.

libstdc++-v3/ChangeLog:

	* testsuite/17_intro/names.cc (func): Undef on AIX.

libstdc++-v3/testsuite/17_intro/names.cc

@@ -203,6 +203,8 @@
 #undef y
 // <sys/var.h> defines vario::v
 #undef v
+// <sys/timer.h> defines trb::func and cputime_tmr::func
+#undef func
 #endif
 
 #ifdef __APPLE__