Re: (toplevel patch) Fix multilib.out dependencies and related problems.

[DJ Delorie <dj@redhat.com>]

> Removed xgcc and ran 'make'; gcc rebuilt it, and target libs were 
> reconfigured and built. 

That shouldn't happen.  Use move-if-change to update one common
multilib.out, so that if the list of multilibs doesn't change,
*nothing* gets reconfigured or rebuilt.  We want to trigger a *check*
when gcc changes, but only actually *reconfigure* if needed.

I'm wondering if the common multilib.out target should depend on the
all-gcc phony target; we kinda want it to run every time we check the
gcc subdir, because we don't know if something else besides xgcc
affects the specs (which affects multilib.out).  We can get away with
this if we use move-if-change.