Support building all variants.

Bug: 143217452
Test: cd external/rust; mma; atest in all TEST_MAPPING subdirs
Change-Id: I2642a656f3dfb91b5d3f1ee0393a89007d320061
diff --git a/src/lib.rs b/src/lib.rs
index 3929b02..7b01db0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -253,7 +253,7 @@
 #![no_std]
 #![doc(html_root_url = "https://docs.rs/bitflags/1.2.1")]
 
-#[cfg(test)]
+// ANDROID: Unconditionally use std to allow building as a dylib
 #[macro_use]
 extern crate std;