codegen: memmove/memset cannot be non-temporal

compiler/rustc_codegen_llvm/src/builder.rs

@@ -976,6 +976,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         align: Align,
         flags: MemFlags,
     ) {
+        assert!(!flags.contains(MemFlags::NONTEMPORAL), "non-temporal memset not supported");
         let is_volatile = flags.contains(MemFlags::VOLATILE);
         unsafe {
             llvm::LLVMRustBuildMemSet(