Don't copy host cross variants to testcases

Checking for os == BuildOS isn't sufficient if we are also cross
compiling to other architectures for that OS, for example when
BuildOS is linux_musl and we are building for x86_64 and cross
compiling to arm64.  Also skip variants that are HostCross.

Bug: 236052820
Test: linux musl x86_64 + arm64 build
Change-Id: I58ce0d8cbfa7c3e209d22c03e49f6d094ff5e107
diff --git a/build/art.go b/build/art.go
index 8272335..c39b7e3 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() != ctx.Config().BuildOS || ctx.Module().IsSkipInstall() {
+	if ctx.Os() != ctx.Config().BuildOS || ctx.Target().HostCross || ctx.Module().IsSkipInstall() {
 		return
 	}