[g++, testsuite] XFAIL thread_local-order2.C on newlib

testsuite/
	* g++.dg/tls/thread_local-order2.C: XFAIL on newlib.

As commented by Mike, it's better that newlib support this feature, tracked by

  https://sourceware.org/bugzilla/show_bug.cgi?id=21325

From-SVN: r246563