Replace android.BuildOs with Config.BuildOS

Replace the android.BuildOs constant with Config.BuildOS so that it
can vary based on the product config.

Bug: 190084016
Test: all Soong tests
Change-Id: Ia67f872d8b2ab788747a22e3a9659dc21c9775cd
diff --git a/java/dexpreopt_test.go b/java/dexpreopt_test.go
index b25dece..8dc7b79 100644
--- a/java/dexpreopt_test.go
+++ b/java/dexpreopt_test.go
@@ -16,6 +16,7 @@
 
 import (
 	"fmt"
+	"runtime"
 	"testing"
 
 	"android/soong/android"
@@ -173,9 +174,9 @@
 }
 
 func TestDex2oatToolDeps(t *testing.T) {
-	if android.BuildOs != android.Linux {
+	if runtime.GOOS != "linux" {
 		// The host binary paths checked below are build OS dependent.
-		t.Skipf("Unsupported build OS %s", android.BuildOs)
+		t.Skipf("Unsupported build OS %s", runtime.GOOS)
 	}
 
 	preparers := android.GroupFixturePreparers(