Add attr/xattr.h header

Author: gnzlbg

libc-test/build.rs

@@ -1228,6 +1228,7 @@ fn test_android(target: &str) {
     headers! { cfg:
                "arpa/inet.h",
                "asm/mman.h",
+               "attr/xattr.h",
                "ctype.h",
                "dirent.h",
                "dlfcn.h",
@@ -1399,12 +1400,8 @@ fn test_android(target: &str) {
 
     cfg.skip_const(move |name| {
         match name {
-            // Android uses old kernel headers
-            // These are constants used in getrandom syscall
-            // "GRND_NONBLOCK" | "GRND_RANDOM" => true,
-
-            // Defined by libattr not libc on linux (hard to test).
-            // See constant definition for more details.
+            // Not part of any system headers - should be removed
+            // or deprecated.
             // "ENOATTR" => true,
 
             // FIXME: still necessary?