[Bug libstdc++/51906] thread lock test failures on darwin11 under Xcode 4.2

[howarth at nitro dot med.uc.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51906

--- Comment #15 from Jack Howarth <howarth at nitro dot med.uc.edu> 2012-01-28 
23:14:09 UTC ---
Note that all three failing test cases on Lion pass if I append -D_XOPEN_SOURCE
to the compilation flags for those tests.