cmd/dist: fix negative test filtering

std and race bench tests fail to check against t.runRxWant, so what
should be negative filters act as positive filters.

Fixes #19239

Change-Id: Icf02b2192bcd806a162fca9fb0af68a27ccfc936
Reviewed-on: https://go-review.googlesource.com/37336
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/dist/test.go

@@ -263,7 +263,7 @@ var (
 
 func (t *tester) registerStdTest(pkg string) {
 	testName := "go_test:" + pkg
-	if t.runRx == nil || t.runRx.MatchString(testName) {
+	if t.runRx == nil || t.runRx.MatchString(testName) == t.runRxWant {
 		stdMatches = append(stdMatches, pkg)
 	}
 	t.tests = append(t.tests, distTest{
@@ -299,7 +299,7 @@ func (t *tester) registerStdTest(pkg string) {
 
 func (t *tester) registerRaceBenchTest(pkg string) {
 	testName := "go_test_bench:" + pkg
-	if t.runRx == nil || t.runRx.MatchString(testName) {
+	if t.runRx == nil || t.runRx.MatchString(testName) == t.runRxWant {
 		benchMatches = append(benchMatches, pkg)
 	}
 	t.tests = append(t.tests, distTest{