cmd/vet: use default compiler when determining type sizes

Fixes a segfault running vet on alpha.

Patch by Uros Bizjak.

Change-Id: Ia1aea8c1b7b8e53f8ad316e2965732669c1611e0
Reviewed-on: https://go-review.googlesource.com/c/152437
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed