Use config.BuildOS instead of android.BuildOs

android.BuildOs is being replaced with config.BuildOS so that it
can vary based on the product configuration.

Bug: 190084016
Test: m checkbuild
Change-Id: Ic660bd9a34faf323a1458bb88f07b1bc8db7d460
diff --git a/build/art.go b/build/art.go
index a24da80..e606cb2 100644
--- a/build/art.go
+++ b/build/art.go
@@ -305,7 +305,7 @@
 // The 'key' is the file in testcases and 'value' is the path to copy it from.
 // The actual copy will be done in make since soong does not do installations.
 func addTestcasesFile(ctx android.InstallHookContext) {
-	if ctx.Os() != android.BuildOs || ctx.Module().IsSkipInstall() {
+	if ctx.Os() != ctx.Config().BuildOS || ctx.Module().IsSkipInstall() {
 		return
 	}