Make all compiler-builtins symbols hidden

This matches cg_llvm

Fixes #1152

src/driver/mod.rs

@@ -44,13 +44,19 @@ fn predefine_mono_items<'tcx>(
     mono_items: &[(MonoItem<'tcx>, (RLinkage, Visibility))],
 ) {
     cx.tcx.sess.time("predefine functions", || {
+        let is_compiler_builtins = cx.tcx.is_compiler_builtins(LOCAL_CRATE);
         for &(mono_item, (linkage, visibility)) in mono_items {
             match mono_item {
                 MonoItem::Fn(instance) => {
                     let name = cx.tcx.symbol_name(instance).name.to_string();
                     let _inst_guard = crate::PrintOnPanic(|| format!("{:?} {}", instance, name));
                     let sig = get_function_sig(cx.tcx, cx.module.isa().triple(), instance);
-                    let linkage = crate::linkage::get_clif_linkage(mono_item, linkage, visibility);
+                    let linkage = crate::linkage::get_clif_linkage(
+                        mono_item,
+                        linkage,
+                        visibility,
+                        is_compiler_builtins,
+                    );
                     cx.module.declare_function(&name, linkage, &sig).unwrap();
                 }
                 MonoItem::Static(_) | MonoItem::GlobalAsm(_) => {}