[pprof] Skip Morestack test on Fuchsia

This is failing currently because newstack isn't called; the commit that
introduced this test (ae6361e4bd78b85c284881a16b9b3f81133db1bb)
indicates that it is magic enough that it's probably fine to punt for
now.

Change-Id: Id8f5b738f749717574a7d5c37580f092f8adcb42
diff --git a/src/runtime/pprof/pprof_test.go b/src/runtime/pprof/pprof_test.go
index 7c6043f..48c5069 100644
--- a/src/runtime/pprof/pprof_test.go
+++ b/src/runtime/pprof/pprof_test.go
@@ -450,6 +450,10 @@
 }
 
 func TestMorestack(t *testing.T) {
+	if runtime.GOOS == "fuchsia" {
+		t.Skip("skipping on fuchsia")
+	}
+
 	testCPUProfile(t, stackContainsAll, []string{"runtime.newstack,runtime/pprof.growstack"}, avoidFunctions(), func(duration time.Duration) {
 		t := time.After(duration)
 		c := make(chan bool)