install_toolchain: cleanup gcc logic.

Since slots for gcc are no longer supported, we don't need
to account for multiple versions. This unifies the gcc
handling logic with that of the other packages.

BUG=chromium:878860
TEST=precq, manual

Change-Id: Ibe477fe4734884d9b98a3bddd70acd7060c6ce8d
Reviewed-on: https://chromium-review.googlesource.com/1195009
Commit-Ready: Alex Klein <saklein@chromium.org>
Tested-by: Alex Klein <saklein@chromium.org>
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed