Add all possible features (NEON, FP) to aarch64 android target.

Author: Nercury

src/librustc_back/target/aarch64_linux_android.rs

@@ -13,6 +13,9 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::android_base::opts();
     base.max_atomic_width = 128;
+    // As documented in http://developer.android.com/ndk/guides/cpu-features.html
+    // the neon (ASIMD) and FP must exist on all android aarch64 targets.
+    base.features = "+neon,+fp-armv8".to_string();
     Target {
         llvm_target: "aarch64-linux-android".to_string(),
         target_endian: "little".to_string(),