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/android/arch_test.go b/android/arch_test.go
index 8525b03..7ec050f 100644
--- a/android/arch_test.go
+++ b/android/arch_test.go
@@ -36,6 +36,7 @@
 }
 
 func TestFilterArchStruct(t *testing.T) {
+	t.Parallel()
 	tests := []struct {
 		name     string
 		in       interface{}
@@ -274,6 +275,7 @@
 }
 
 func TestArchMutator(t *testing.T) {
+	t.Parallel()
 	var buildOSVariants []string
 	var buildOS32Variants []string
 	switch runtime.GOOS {
@@ -385,6 +387,7 @@
 }
 
 func TestArchMutatorNativeBridge(t *testing.T) {
+	t.Parallel()
 	bp := `
 		// This module is only enabled for x86.
 		module {