runtime: skip TestSegv traceback check on 386

The VDSO (__kernel_vsyscall) is reachable via
asmcgocall(cgo_start_thread) on linux-386, which causes traceback to
throw.

Fixes #49182.
For #50504.

Change-Id: Idb78cb8de752203ce0ed63c2dbd2d12847338688
Reviewed-on: https://go-review.googlesource.com/c/go/+/376656
Reviewed-by: Cherry Mui <[email protected]>
Trust: Michael Pratt <[email protected]>
Run-TryBot: Michael Pratt <[email protected]>

Author: prattmic

src/runtime/crash_cgo_test.go

@@ -625,12 +625,20 @@ func TestSegv(t *testing.T) {
 				// TODO(golang.org/issue/49182): Skip, runtime
 				// throws while attempting to generate
 				// traceback.
-			default:
-				nowant := "runtime: "
-				if strings.Contains(got, nowant) {
-					t.Errorf("unexpectedly saw %q in output", nowant)
+				return
+			case "linux":
+				if runtime.GOARCH == "386" {
+					// TODO(golang.org/issue/50504): Skip,
+					// runtime throws while attempting to
+					// generate traceback from VDSO call
+					// via asmcgocall.
+					return
 				}
 			}
+			nowant := "runtime: "
+			if strings.Contains(got, nowant) {
+				t.Errorf("unexpectedly saw %q in output", nowant)
+			}
 		})
 	}
 }