Support building all variants.

Bug: 143217452
Test: cd external/rust; mma; atest in all TEST_MAPPING subdirs
Change-Id: I7728eab43699cab2ed266b7f5bc22e5f99731d69
diff --git a/Android.bp b/Android.bp
index cea0f97..9ed8e0b 100644
--- a/Android.bp
+++ b/Android.bp
@@ -1,6 +1,6 @@
 // This file is generated by cargo2android.py --run --device.
 
-rust_library_rlib {
+rust_library {
     name: "libfutures_task",
     host_supported: true,
     crate_name: "futures_task",
@@ -12,7 +12,7 @@
         "once_cell",
         "std",
     ],
-    rlibs: [
+    rustlibs: [
         "libonce_cell",
     ],
 }