Rollup merge of rust-lang#40317 - malbarbo:update-libc, r=alexcrichton

Update libc to 0.2.21

Update to include android aarch64 and x86 improvements.

Author: frewsxcv

src/liblibc

@@ -14,22 +14,24 @@
 
 use fmt;
 
-#[cfg(any(target_os = "android",
-          target_os = "emscripten",
+#[cfg(any(target_os = "emscripten",
           all(target_os = "linux", any(target_arch = "aarch64",
                                        target_arch = "arm",
                                        target_arch = "powerpc",
                                        target_arch = "powerpc64",
                                        target_arch = "s390x")),
+          all(target_os = "android", any(target_arch = "aarch64",
+                                         target_arch = "arm")),
           all(target_os = "fuchsia", target_arch = "aarch64")))]
 #[stable(feature = "raw_os", since = "1.1.0")] pub type c_char = u8;
-#[cfg(not(any(target_os = "android",
-              target_os = "emscripten",
+#[cfg(not(any(target_os = "emscripten",
               all(target_os = "linux", any(target_arch = "aarch64",
                                            target_arch = "arm",
                                            target_arch = "powerpc",
                                            target_arch = "powerpc64",
                                            target_arch = "s390x")),
+              all(target_os = "android", any(target_arch = "aarch64",
+                                             target_arch = "arm")),
               all(target_os = "fuchsia", target_arch = "aarch64"))))]
 #[stable(feature = "raw_os", since = "1.1.0")] pub type c_char = i8;
 #[stable(feature = "raw_os", since = "1.1.0")] pub type c_schar = i8;