RFA: Fix copying of libgcc multilibs

[David Daney]

Richard Sandiford wrote:

> "all-multi" therefore installs each multilib's files into
> "$objdir/gcc/$mlib/...", as expected.  But the default multilib's
> "install" rule is itself recursive, so "all" recurses again, this time
> installing with DESTDIR="../../gcc".  For non-default multilibs, this
> means installing in "$objdir/$target_alias/$mlib/libgcc/../../gcc/".
> I noticed this because libjava's testsuite was finding
> "$objdir/$target_alias/gcc" instead of "$objdir/gcc", and was then
> trying to run "$objdir/$target_alias/gcc/xgcc --print-multi-lib".
> 
> I wasn't sure whether we should add an "install-leaf" rule,
> override MULTIDIRS, override MULTIDO, or something else,
> but Dan voted for the first.
> 
> Bootstrapped & regression-tested x86_64-linux-gnu.  Also regression-tested
> on mips64-linux-gnu.  OK to install?
> 
> Richard
> 
> 
> libgcc/
> 	* Makefile.in (all): Use install-leaf rather than install.
> 	(install): Split most of the rule into...
> 	(install-leaf): ...this new one.
> 

Thanks Richard.  This one was really bothering me.

FWIW, I can confirm that this is a real problem.

David Daney