cmd/dist: run limited tests in race and libgcc=none modes

Mostly we just care that the test binaries link and start up.
No need to run the full test suites.

Takes 12% off my all.bash run time.

For #10571.

Change-Id: I01af618f3d51deb841ea638424e1389a2df7d746
Reviewed-on: https://go-review.googlesource.com/18086Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>

src/cmd/dist/test.go

@@ -386,11 +386,15 @@ func (t *tester) registerTests() {
 		}
 
 		pkg := pkg
+		var run string
+		if pkg == "net" {
+			run = "TestTCPStress"
+		}
 		t.tests = append(t.tests, distTest{
 			name:    "nolibgcc:" + pkg,
 			heading: "Testing without libgcc.",
 			fn: func() error {
-				return t.dirCmd("src", "go", "test", "-short", "-ldflags=-linkmode=internal -libgcc=none", t.tags(), pkg).Run()
+				return t.dirCmd("src", "go", "test", "-short", "-ldflags=-linkmode=internal -libgcc=none", t.tags(), pkg, "-run="+run).Run()
 			},
 		})
 	}
@@ -869,7 +873,7 @@ func (t *tester) raceTest() error {
 	if err := t.dirCmd("src", "go", "test", "-race", "-run=Output", "runtime/race").Run(); err != nil {
 		return err
 	}
-	if err := t.dirCmd("src", "go", "test", "-race", "-short", "flag", "os/exec").Run(); err != nil {
+	if err := t.dirCmd("src", "go", "test", "-race", "-short", "-run=TestParse|TestEcho", "flag", "os/exec").Run(); err != nil {
 		return err
 	}
 	if t.cgoEnabled {
@@ -882,7 +886,7 @@ func (t *tester) raceTest() error {
 	}
 	if t.extLink() {
 		// Test with external linking; see issue 9133.
-		if err := t.dirCmd("src", "go", "test", "-race", "-short", "-ldflags=-linkmode=external", "flag", "os/exec").Run(); err != nil {
+		if err := t.dirCmd("src", "go", "test", "-race", "-short", "-ldflags=-linkmode=external", "-run=TestParse|TestEcho", "flag", "os/exec").Run(); err != nil {
 			return err
 		}
 	}