misc/cgo/test: disable sigaltstack test on darwin/386

It doesn't work there ("out of memory") and doesn't really matter.
Fixes build (now that we enable cgo on the darwin/386 builder.)

Change-Id: I1d91e51ecb88c54eae39ac9a76f2c0b4e45263b0
Reviewed-on: https://go-review.googlesource.com/19004
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

misc/cgo/test/sigaltstack.go

@@ -57,6 +57,8 @@ func testSigaltstack(t *testing.T) {
 	switch {
 	case runtime.GOOS == "solaris", runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64"):
 		t.Skipf("switching signal stack not implemented on %s/%s", runtime.GOOS, runtime.GOARCH)
+	case runtime.GOOS == "darwin" && runtime.GOARCH == "386":
+		t.Skipf("sigaltstack fails on darwin/386")
 	}
 
 	C.changeSignalStack()