[PATCH] Add support for --with-arch configure option

[Roland McGrath]

If you aren't adding new sysdeps/CPU/SUBTYPE directories in libc or a libc
add-on, then there is no reason to use --with-cpu.  Just put whatever -mfoo
switches you like into CC when running configure.

As of GCC 4.3, -mcpu= and -mtune= are what's documented for powerpc, and
-march= is not documented as available.  In GCC 4.1, -march= is not
available for powerpc.

We're only going to have one configure switch related to this, as Ulrich
said.  What it does needs to work for all the supported GCC versions with
which people build libc using --with-cpu today.  We support all since 3.4,
though I presume there is a small subset of GCC version + machine pairs on
which anyone needs --with-cpu to work.


Thanks,
Roland