Replace FutureApiLevel with an ApiLevel.

Keeping the int constant around for now as FutureApiLevelInt because
it's still useful in places that haven't adopted ApiLevel yet for
testing if their non-ApiLevel API level is current or not.

Test: treehugger
Bug: http://b/154667674
Change-Id: I47a7012703f41fdeb56f91edf9c83afa93042deb
diff --git a/cc/ndk_library.go b/cc/ndk_library.go
index 4c6d98c..5682d1c 100644
--- a/cc/ndk_library.go
+++ b/cc/ndk_library.go
@@ -118,8 +118,8 @@
 			versionStrs = append(versionStrs, version.String())
 		}
 	}
-	versions = append(versions, android.CurrentApiLevel)
-	versionStrs = append(versionStrs, android.CurrentApiLevel.String())
+	versions = append(versions, android.FutureApiLevel)
+	versionStrs = append(versionStrs, android.FutureApiLevel.String())
 
 	modules := ctx.CreateVariations(versionStrs...)
 	for i, module := range modules {