Commit 52ba784d replaced $(STRIP_OPT) with $(STRIP) in some
places (for example, Makefile.target), but not all of them.
There are a few places remain in main Makefile which still
uses $(STRIP_OPT).  Replace these places with $(STRIP) too.

While at it, simplify variable pattern substitution of the
surrounding places, change $(patsubst pat,rep,$(var)) into
$(var:pat=rep) which is much easier to read (this is probably
a good idea to do everywhere).
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>
Cc: Fam Zheng <famz@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>