builder: Add helper to get the path to a sysroot wrapper.

Nits from https://chromium-review.googlesource.com/#/c/268399/.

BUG=None
TEST=unittests.

Change-Id: I9b6ade292ac215fc83bb827ba939b1a717c57c48
Reviewed-on: https://chromium-review.googlesource.com/268679
Reviewed-by: Gilad Arnold <garnold@chromium.org>
Commit-Queue: Bertrand Simonnet <bsimonnet@chromium.org>
Tested-by: Bertrand Simonnet <bsimonnet@chromium.org>
1 file changed