somewhat-auto-rebuilding libgcc.a with -fhonor-std

[Benjamin Kosnik]

> How about 
>   o   '--enable-libgcc-rebuild=path/to/gcc/builddir' turns it on
>   o   'make'  by default does the work

Sounds great. I like this approach better.

> It looks like the only difficulty is going to be the re-installation
> of libgcc.a.  We could invoke gcc's "make install-libgcc" ourselves,
> but we can't make any backup copies or set up any symlinks to let the
> user switch back and forth (where libgcc.a gets placed isn't known to us
> unless we try grepping it out of their Makefile).  Do we require the user
> to do the installation?  (I'd vote yes.)

Hmm. What about installing the rebuilt libgcc.a in bld-libstdc++/src/.libs
and adjusting paths so that it's picked up before the one in
GCC_EXEC_PREFIX? IT would be nice not to smash the old libgcc.a install.

If there is no clean way to do it, just specify directions for the manual
install at the end, I guess.

Does anybody else have any suggestions? 

> Yeah, we need both build and src.  Not /all/ of both, but I'm not going to
> try and discover the minimum sets of code, because I'm coming down with
> a cold.  I'll just add a note to the docs saying, "If you've already
> removed the builddir, you're being a chump.  Reconfigure gcc same as
> before and then either read <my first email message> or just rebuild
> everything and re-run 'make' in libstdc++."

sounds good, except for the cold part. Watch out, the flu that is going
around is really yukky.

-Benjamin