Make lots of tests run in parallel

Putting t.Parallel() in each test makes them run in parallel.
Additional t.Parallel() could be added to each subtest, although
that requires making a local copy of the loop variable for
table driven tests.

Test: m checkbuild
Change-Id: I5d9869ead441093f4d7c5757f2447385333a95a4
diff --git a/cc/compiler_test.go b/cc/compiler_test.go
index c301388..cf553bd 100644
--- a/cc/compiler_test.go
+++ b/cc/compiler_test.go
@@ -19,6 +19,7 @@
 )
 
 func TestIsThirdParty(t *testing.T) {
+	t.Parallel()
 	shouldFail := []string{
 		"external/foo/",
 		"vendor/bar/",