[compiler_wrapper] explicitly enables `libgcc` as the unwindlib

This is in preparation for our migration to libunwind.

BUG=b:187785190
TEST=Tested locally and on CQ

Disallow-Recycled-Builds: test-failures
Change-Id: I1b11d54de3d9550086ead05c3880f149e2e2f839
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2945100
Tested-by: Christopher Di Bella <cjdb@google.com>
Tested-by: Luis Lozano <llozano@chromium.org>
Auto-Submit: Christopher Di Bella <cjdb@google.com>
Commit-Queue: Luis Lozano <llozano@chromium.org>
Reviewed-by: Luis Lozano <llozano@chromium.org>
21 files changed