Update x86_64_uwp_windows_msvc.rs

Updated x86_64-uwp-windows-msvc to use CMPXCHG16B and SSE3

Author: CKingX

compiler/rustc_target/src/spec/targets/x86_64_uwp_windows_msvc.rs

@@ -3,8 +3,9 @@ use crate::spec::{base, Target};
 pub fn target() -> Target {
     let mut base = base::windows_uwp_msvc::opts();
     base.cpu = "x86-64".into();
+    base.features = "+cx16,+sse3".into();
     base.plt_by_default = false;
-    base.max_atomic_width = Some(64);
+    base.max_atomic_width = Some(128);
 
     Target {
         llvm_target: "x86_64-pc-windows-msvc".into(),