Always include host variants in the sdk snapshot

Host tools (and variants in general) should not fall under the purview
of min_sdk_version check. These do not exist on device, so
min_sdk_version check would not make such sense.

This is prework for migrating min_sdk_version from type SdkSpec to
ApiLevel.

Test: go test ./sdk
Bug: 208456999

Change-Id: I2fd822a223d1dc5e290d4a1ebf304fe47a5b0416

sdk/update.go

@@ -357,6 +357,12 @@ func (s *sdk) buildSnapshot(ctx android.ModuleContext, sdkVariants []*sdk) {
 		// If the minApiLevel of the member is greater than the target API level then exclude it from
 		// this snapshot.
 		exclude := memberVariantDep.minApiLevel.GreaterThan(targetApiLevel)
+		// Always include host variants (e.g. host tools) in the snapshot.
+		// Host variants should not be guarded by a min_sdk_version check. In fact, host variants
+		// do not have a `min_sdk_version`.
+		if memberVariantDep.Host() {
+			exclude = false
+		}
 
 		addMember(name, export, exclude)
 
@@ -1263,6 +1269,11 @@ type sdkMemberVariantDep struct {
 	minApiLevel android.ApiLevel
 }
 
+// Host returns true if the sdk member is a host variant (e.g. host tool)
+func (s *sdkMemberVariantDep) Host() bool {
+	return s.variant.Target().Os.Class == android.Host
+}
+
 var _ android.SdkMember = (*sdkMember)(nil)
 
 // sdkMember groups all the variants of a specific member module together along with the name of the