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>
diff --git a/libgo/go/cmd/vet/types.go b/libgo/go/cmd/vet/types.go
index 5f8e481..60b6125 100644
--- a/libgo/go/cmd/vet/types.go
+++ b/libgo/go/cmd/vet/types.go
@@ -310,4 +310,4 @@
 	return true
 }
 
-var archSizes = types.SizesFor("gc", build.Default.GOARCH)
+var archSizes = types.SizesFor(build.Default.Compiler, build.Default.GOARCH)