bin/mklib: Clear CDPATH to avoid damaging expand_archive output

bin/mklib: Clear CDPATH to avoid damaging expand_archive output

The bash 'cd' command tends to emit random stuff to stdout when the
CDPATH variable is set, so clear it to keep extra filenames from being
emitted from the expand_archive function, which would otherwise cause
mklib to fail.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Dan Nicholson <dbn.lists@gmail.com>
Signed-off-by: Brian Paul <brianp@vmware.com>