un-xfail 12658_thread-1.cc on non-linux platforms

[Richard Earnshaw]

On Sat, 2004-10-30 at 01:53, Geoffrey Keating wrote:
> As far as I can tell from the mailing list, this was xfailed because
> of a linux libc bug, and it passes on Darwin for me.
> 
> Tested with 'make check-libstdc++-v3' on Darwin.

This test will never run on embedded systems that don't have pthreads. 
If you are going to enable it, the it should be enabled in the same way
as the pthreads tests are.

R.