MT-safe EH diffs against 1.00

[Jason Merrill]

Thanks.  Please update this patch to egcs-971207; several things have
changed.  For one, the dwarf2 code no longer uses __eh_pc.  Which is a
binary incompatibility, now that I think about it.

Also, using a libcall to return a pointer will currently break on targets
that return pointers in a different register, because Pmode == some integer
mode.  Jim seemed to think that using libcall for these sorts of functions
was a mistake in any case; why was that, again?  And then how is
memcpy_libfunc supposed to work?

Jason