Rollup merge of #39724 - malbarbo:android, r=alexcrichton

Allow rustc data structures compile to android

flock structure is defined in asm*/fcntl.h. This file on android is
generated from the linux kernel source, so they are the same.

src/librustc_data_structures/flock.rs

@@ -27,7 +27,7 @@ mod imp {
     use std::io;
     use libc;
 
-    #[cfg(target_os = "linux")]
+    #[cfg(any(target_os = "linux", target_os = "android"))]
     mod os {
         use libc;