Add the ability to select on arch

Bug: 323382414
Test: go test
Change-Id: I0d4cf391a1a625c5160456db1f4f7fa424c2141e

android/arch_module_context.go

@@ -35,6 +35,7 @@ type ArchModuleContext interface {
 type archModuleContext struct {
 	// TODO: these should eventually go through a (possibly cached) provider like any other configuration instead
 	//  of being special cased.
+	ready         bool
 	os            OsType
 	target        Target
 	targetPrimary bool
@@ -42,6 +43,13 @@ type archModuleContext struct {
 	primaryArch   bool
 }
 
+// ArchReady returns true if the arch mutator has run on the module. Before this returns
+// true, the module essentially doesn't have an arch and cannot make decisions based on
+// architecture.
+func (a *archModuleContext) ArchReady() bool {
+	return a.ready
+}
+
 func (a *archModuleContext) Target() Target {
 	return a.target
 }