runtime: ignore TestCgoPprofPIE test failures on Alpine

Updates #19938
Updates #18243

Change-Id: Ib6e704c0a5d596bdfaa6493902d2528bec55bf16
Reviewed-on: https://go-review.googlesource.com/41628
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/crash_cgo_test.go

@@ -282,6 +282,10 @@ func testCgoPprof(t *testing.T, buildArg, runArg string) {
 
 	got, err := testEnv(exec.Command(exe, runArg)).CombinedOutput()
 	if err != nil {
+		if testenv.Builder() == "linux-arm64-alpine" {
+			// See Issue 18243 and Issue 19938.
+			t.Skipf("Skipping failing test on Alpine (golang.org/issue/18243). Ignoring error: %v", err)
+		}
 		t.Fatal(err)
 	}
 	fn := strings.TrimSpace(string(got))