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

androidmk/parser/parser_test.go

@@ -37,6 +37,7 @@ var parserTestCases = []struct {
 }
 
 func TestParse(t *testing.T) {
+	t.Parallel()
 	for _, test := range parserTestCases {
 		t.Run(test.name, func(t *testing.T) {
 			p := NewParser(test.name, bytes.NewBufferString(test.in))