MT safe exception diffs

[John Carr]

> With these changes gcc is built on Solaris to use multilibs to
> compile both Solaris threads and pthreads versions of libgcc.

You only need one version of the exception library: Solaris threads
and pthreads are compatible.  If libgcc uses threads and the program
uses pthreads it will still work.  If you want to support Solaris 2.4
you should use -lthreads in libgcc, otherwise use the one that has the
features you want.