kbuild: move objtool_args back to scripts/Makefile.build

[ Upstream commit 8f0c32c7 ]

Commit b1a1a1a0 ("kbuild: lto: postpone objtool") moved objtool_args
to Makefile.lib, so the arguments can be used in Makefile.modfinal as
well as Makefile.build.

With commit 850ded46 ("kbuild: Fix TRIM_UNUSED_KSYMS with
LTO_CLANG"), module LTO linking came back to scripts/Makefile.build
again.

So, there is no more reason to keep objtool_args in a separate file.

Get it back to the original place, close to the objtool command.

Remove the stale comment too.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>