documentation and new --enable flags

[Phil Edwards]

> > can the rebuild of libgcc.a take into account CXXFLAGS?
>
> I tried this approach, and the only method I could think of that would
> be certain to get the same CXXFLAGS is to (literally) grep them out of
> src/Makefile*, since they aren't ever accumulated anywhere else.  This is
> possible, of course, but seems kind of a hack.

My brain is a large hunk of cheese.  Here's a different way of doing it
(also a hack).

I first "tried that approach" when the rebuild was done as an external
script.  Now that the rebuild is done at the same time as the main build,
/of course/ CXXFLAGS can be used to override the defaults.  I have a patch
(now) that does this.  Duh.

BUT the 'real' CXXFLAGS is still only accumulated in src/Makefile,
from the decisions of --enable/--disable -namespaces and -debug, and
from the "how optimal can we be" checking of the compiler version.
Those accumulated settings still won't be passed on to the rebuild,
since they're all done in a "lower" Makefile.

Not really a problem in the default case; the main build will get the
specific -g and -O values that we figure out, while the rebuild gets the
values that GCC's configure figured out.  If the user specifies CXXFLAGS
in the make environment, both the main build and the rebuild will use
that CXXFLAGS.


If we /really/ want them to match, the make target that performs the
rebuild could be moved from Makefile.am down to src/Makefile.am.  They'd
all get the same flags then.  Dunno if that's an appropriate move though.

Phil