Refactor shared_timed_mutex tests.

First I removed all of the uses of _LIBCPP_STD_VER and added LIT UNSUPPORTED tags to prevent the tests from being run in older standard dialects.
Second I increased the time tolerances used in some tests when testing with Thread Sanitizer because thread sanitizer make these tests take longer.

git-svn-id: 91177308-0d34-0410-b5e6-96231b3b80d8
21 files changed