UPSTREAM: objtool: Install libsubcmd in build

Including from tools/lib can create inadvertent dependencies. Install
libsubcmd in the objtool build and then include the headers from
there.

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20230126190606.40739-2-irogers@google.com


Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Bug: 336872347
Bug: 335829879
Test: build x86_64 kernel with glibc 2.38
Change-Id: Id09c5b222519073214dbc01e151e59b18afb1ea8
(cherry picked from commit bdb8bf7d)
Signed-off-by: Yifan Hong <elsk@google.com>