Remove config.cache files when reconfiguring at top level

[Andreas Schwab]

Nick Clifton <nickc@redhat.com> writes:

>  4. User runs make distclean.
>     There are no Makefiles present in the sub-directories so
>     the config.cache files are left intact.

So clean them here.  That's the only correct place to do it.  Only
distclean is allowed to remove configuration-recording files.

Andreas.

-- 
Andreas Schwab, schwab@redhat.com
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