Add missing "max_atomic_width" to new armv7 android target.

Author: Nercury

src/librustc_back/target/armv7_linux_androideabi.rs

@@ -13,6 +13,7 @@ use target::Target;
 pub fn target() -> Target {
     let mut base = super::android_base::opts();
     base.features = "+v7,+thumb2,+vfp3,+d16".to_string();
+    base.max_atomic_width = 64;
 
     Target {
         llvm_target: "armv7-none-linux-android".to_string(),