[toplevel PATCH] [RFC] create a staging area for new-bootstrap stages

["Paolo Bonzini" <bonzini at gnu dot org>]

As a prerequisite for three-staging libiberty, gas, etc., this patch changes
the way a toplevel bootstrap prepares the successive stage.  Instead of
using the xgcc driver in the previous build directory, this one installs gcc
into a staging area which is to hold as well gas, ld, and so on.  The
staging area toplevel subdirectory is named stage1 or stage2.

The patch requires the previous flags-to-pass-shorten.patch, otherwise
recursive makes override the special --prefix that is established for
stage1 and stage2.

I have not tested it very much, as I could not wait for all-stage3-gcc and
compare to finish.  It went fine up to the point I let it run.  Given that
toplevel patches are usually made in a very incremental way, I'll ask anyway
if it is "Ok for mainline if comparison succeeds?", but I'd understand as
well delaying this until I have a combined tree bootstrap mostly working.

Next steps:
- modifying USUAL_*_FOR_TARGET to find previous stage binutils & co
- generating maybe-dependencies for bootstrapped modules
- generating {all,configure}-stageN-MODULE for bootstrapped modules
- adding clear and distclean targets
- adding other bells and whistles such as quickstrap and bubblestrap
- enabling toplevel bootstrap with a toplevel configure switch
- adding four stage bootstrap
- adding profiledbootstrap

and maybe some more I did not think about. :-)

Paolo

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