Support no configured device architectures

There are some builds where we only want to build host tools, and we may
not have a valid device configuration. Support 0 device architectures
and modules that don't have any configured way to build.

Change-Id: I732251e1cd3cdbfafbc6ef6a550e33e653876f7c

android/arch.go

@@ -435,6 +435,11 @@ func ArchMutator(mctx BottomUpMutatorContext) {
 		moduleTargets = append(moduleTargets, targets...)
 	}
 
+	if len(moduleTargets) == 0 {
+		module.base().commonProperties.Enabled = boolPtr(false)
+		return
+	}
+
 	targetNames := make([]string, len(moduleTargets))
 
 	for i, target := range moduleTargets {
@@ -762,10 +767,7 @@ func decodeTargetProductVariables(config Config) (map[OsClass][]Target, error) {
 		}
 	}
 
-	if variables.DeviceArch == nil {
+	if variables.DeviceArch != nil && *variables.DeviceArch != "" {
-		return nil, fmt.Errorf("No device primary architecture set")
-	}
-
 		addTarget(Android, *variables.DeviceArch, variables.DeviceArchVariant,
 			variables.DeviceCpuVariant, variables.DeviceAbi)
 
@@ -779,6 +781,7 @@ func decodeTargetProductVariables(config Config) (map[OsClass][]Target, error) {
 				deviceArches[1].Arch.Native = false
 			}
 		}
+	}
 
 	if targetErr != nil {
 		return nil, targetErr

cc/cc.go

@@ -909,7 +909,7 @@ func (c *Module) depsMutator(actx android.BottomUpMutatorContext) {
 }
 
 func depsMutator(ctx android.BottomUpMutatorContext) {
-	if c, ok := ctx.Module().(*Module); ok {
+	if c, ok := ctx.Module().(*Module); ok && c.Enabled() {
 		c.depsMutator(ctx)
 	}
 }