misc/cgo/test: skip Test18146 in short mode

Fixes #21219

Change-Id: I1a2ec1afe06586ed33a3a855b77536490cac3a38
Reviewed-on: https://go-review.googlesource.com/121115
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

misc/cgo/test/issue18146.go

@@ -22,6 +22,10 @@ import (
 )
 
 func test18146(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping in short mode")
+	}
+
 	if runtime.GOOS == "darwin" {
 		t.Skipf("skipping flaky test on %s; see golang.org/issue/18202", runtime.GOOS)
 	}
@@ -33,10 +37,6 @@ func test18146(t *testing.T) {
 	attempts := 1000
 	threads := 4
 
-	if testing.Short() {
-		attempts = 100
-	}
-
 	// Restrict the number of attempts based on RLIMIT_NPROC.
 	// Tediously, RLIMIT_NPROC was left out of the syscall package,
 	// probably because it is not in POSIX.1, so we define it here.