[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 #6 from Jack Howarth <howarth at nitro dot med.uc.edu> 2012-01-20 
14:35:52 UTC ---
(In reply to comment #4)
> On x86_64-darwin10 (Xcode 3.2.6) r183290 is OK.
> On powerpc-apple-darwin9 (Xcode 3.1.4) 183218 is OK.

This issue doesn't occur on x86_64-darwin10 with Xcode 4.2 so the problem
seems to be darwin11 specific.