cmd/dist: run testshared on linux/386

Change-Id: I22d40248e83fcad5ab73c0d402183d06e91064c7
Reviewed-on: https://go-review.googlesource.com/16388Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/dist/test.go

@@ -623,7 +623,7 @@ func (t *tester) supportedBuildmode(mode string) bool {
 		return false
 	case "shared":
 		switch pair {
-		case "linux-amd64", "linux-arm", "linux-arm64", "linux-ppc64le":
+		case "linux-386", "linux-amd64", "linux-arm", "linux-arm64", "linux-ppc64le":
 			return true
 		}
 		return false