[PING 6, PATCH] Remove xfail from thread_local-order2.C.

[Dominique d'Humières]

For the record the test XPASS on darwin16 since at least r244095, but not on darwin10:

XPASS: g++.dg/tls/thread_local-order2.C  -std=c++11 execution test
XPASS: g++.dg/tls/thread_local-order2.C  -std=c++14 execution test
XPASS: g++.dg/tls/thread_local-order2.C  -std=c++11 execution test
XPASS: g++.dg/tls/thread_local-order2.C  -std=c++14 execution test

Dominique