[toplevel] Add --enable-bootstrap configure switch

[Alexandre Oliva]

On May 24, 2004, Paolo Bonzini <bonzini@gnu.org> wrote:

> Old-bootstrapped and new-bootstrapped i686-pc-linux-gnu,
> ok for mainline and src?

Not before you post it to gcc-patches@ instead of gcc@ :-)

> +  case "$host:$target:$enable_bootstrap" in
> +    $build:$build:yes | *:no) ;;
> +    *:yes) AC_MSG_ERROR([cannot bootstrap a cross-compiler]) ;;

Actually....  Sometimes you can.

Consider, for example, bootstrapping an i386-pc-linux-gnu native
compiler on an i686-pc-linux-gnu box?

Or bootstrapping a mips-linux-gnu native compiler on a
mips64-linux-gnu box?  Or do it the other way round: start from a
mips-linux-gnu compiler and use that to bootstrap a mips64-linux-gnu
native compiler.

In all but the last case, you can just override --build.  Doing it in
the latter case might even work, but it isn't safe.  At some point we
used to recognize some such cases, but I suppose we can live without
them.

The patch looks good to me.

-- 
Alexandre Oliva             http://www.ic.unicamp.br/~oliva/
Red Hat Compiler Engineer   aoliva@{redhat.com, gcc.gnu.org}
Free Software Evangelist  oliva@{lsd.ic.unicamp.br, gnu.org}