Update x86_64_pc_windows_msvc.rs

As CMPXCHG16B is supported, I updated the max atomic width to 128-bits from 64-bits

Author: CKingX

compiler/rustc_target/src/spec/targets/x86_64_pc_windows_msvc.rs

@@ -5,7 +5,7 @@ pub fn target() -> Target {
     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);
     base.supported_sanitizers = SanitizerSet::ADDRESS;
 
     Target {