Stub out the utimesat emulation logic on Android.

Android always has `utimensat` available, so it is not necessary (or
possible, for that matter) to emulate it. Mark the fallback path as
`unreachable!()`.

crates/wasi-common/yanix/src/sys/linux/filetime.rs

@@ -53,5 +53,8 @@ pub fn utimensat(
         return Err(err);
     }
 
-    super::utimesat::utimesat(dirfd, path, atime, mtime, symlink_nofollow)
+    #[cfg(not(target_os = "android"))]
+    return super::utimesat::utimesat(dirfd, path, atime, mtime, symlink_nofollow);
+    #[cfg(target_os = "android")]
+    unreachable!();
 }

crates/wasi-common/yanix/src/sys/linux/mod.rs

@@ -2,4 +2,5 @@ pub(crate) mod dir;
 pub(crate) mod fadvise;
 pub(crate) mod file;
 pub(crate) mod filetime;
+#[cfg(not(target_os = "android"))]
 pub(crate) mod utimesat;