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

cc/object_test.go

@@ -19,6 +19,7 @@ import (
 )
 
 func TestLinkerScript(t *testing.T) {
+	t.Parallel()
 	t.Run("script", func(t *testing.T) {
 		testCc(t, `
 		cc_object {