ports: clang: error: unsupported option '-dumpspecs'

[b. f.]

> > -dumpspecs is a gcc internal thing that clang will never support (it doesnt use
> > specs). It's wrong for ports to mess with the internals of the compiler and
> > this should be fixed in a clean way.
> >
> > Ie. we have to replace the -dumpspec | grep something with a saner check.
>
>     The fact that gcc -dumpspecs is looked at at all is a really bad
> idea. Do you know which port in the tree is calling this?

As far as I know, in the Ports tree there are only:

editors/emacs
editors/emacs-devel
graphics/OpenEXR
multimedia/vdpau-video

which use it in an ill-conceived (and now probably unnecessary) test
for thread libraries.  However, there are many more instances within
the configuration scripts of various port distfiles, and I do not
think that all of these are protected by tests for gcc*.

b.