build: use `ar` over `gcc-ar`

It has been a sufficiently long time since the last release of binutils
did not automatically enable the LTO plugin. Migrate to `ar` rather than
using the `gcc-ar` build wrapper, which saves us some pain trying to
locate the proper archiver.

Change-Id: I6f8b895d6a470d2b7cd5b98ccb23c54b35d7ad12
Signed-off-by: Chris Kay <chris.kay@arm.com>
1 file changed