Update x86_64_pc_windows_gnullvm.rs

Updated x86_64-pc-windows-gnullvm target to use CMPXCHG16B and SSE3

Author: CKingX

compiler/rustc_target/src/spec/targets/x86_64_pc_windows_gnullvm.rs

@@ -3,9 +3,10 @@ use crate::spec::{base, Cc, LinkerFlavor, Lld, Target};
 pub fn target() -> Target {
     let mut base = base::windows_gnullvm::opts();
     base.cpu = "x86-64".into();
+    base.features = "+cx16,+sse3".into();
     base.plt_by_default = false;
     base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m64"]);
-    base.max_atomic_width = Some(64);
+    base.max_atomic_width = Some(128);
     base.linker = Some("x86_64-w64-mingw32-clang".into());
 
     Target {