devtools/presubmit: report tool-building errors.
devtools/presubmit: report tool-building errors.

If any tool fails to build, there is no point continuing the test.

Change-Id: Ie1590b085881ac3f329097a234edc4855d5b9445

vanadium/go.devtools,vanadium/go.devtools,vanadium/go.devtools