ANDROID: tools/objtool: Pass CFLAGS to libsubcmd build via EXTRA_CFLAGS

The upstream fix is too invasive to backport so we take a similar
fix like http://aosp/2755768

Bug: 355379840
Change-Id: I50258052fbf0c4f8ace7007427037122b4fd02b0
Link: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=cd955bdd


Signed-off-by: Tao Wu <lepton@google.com>
(cherry picked from commit 42e503e2)