wrapper: tweak "toolchain doesn't exist" checks in the updater

When stderr is connected to a tty, equery will output things if it fails
due to being unable to find a package. When it's not, equery will output
nothing on failure.

BUG=None
TEST=./update_compiler_wrapper.sh

Change-Id: I7d16d6a531f1f28fc0157873176d41f6881cd04b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2252550
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Tested-by: George Burgess <gbiv@chromium.org>
1 file changed