go/build: do not parse .syso files

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5786049

src/pkg/go/build/build.go

@@ -483,6 +483,7 @@ Found:
 			// Likely of the form foo_windows.syso, but
 			// the name was vetted above with goodOSArchFile.
 			p.SysoFiles = append(p.SysoFiles, name)
+			continue
 		default:
 			// skip
 			continue