[patch] libstdc++/64368 add configure check for timed mutex operations

[Jonathan Wakely]

This isn't related to the last patch for this bug, except that the PR
is currently being used for all darwin FAILs.

We need to check a configure macro before using
pthread_rwlock_timedrdlock because Darwin doesn't define the
_POSIX_TIMEOUTS option.

Tested x86_64-linux, committed to trunk.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: patch.txt
Type: text/x-patch
Size: 1516 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/libstdc++/attachments/20150127/d70fde0d/attachment.bin>