Remove is_rmc check from monomorphizer (rust-lang#485) (rust-lang#524)

We have changed rmc to always compile the target crate as a library.
This allow us to treat any extern / public function to be used as the
starting point of a proof. Furthermore, it allow us to remove the is_rmc
check that we were using to skip the rust start function generation.
The start function is only generated when we are compiling a bin crate.

Author: celinval

compiler/rustc_monomorphize/src/collector.rs

@@ -319,11 +319,6 @@ pub fn collect_crate_mono_items(
 }
 
 // Temporary function that allow us to skip monomorphizing lang_start.
-fn is_rmc(tcx: TyCtxt<'_>) -> bool {
-    const RMC_STR: &'static str = "rmc";
-    tcx.sess.parse_sess.config.iter().any(|(s, _)| s == &Symbol::intern(RMC_STR))
-}
-
 // Find all non-generic items by walking the HIR. These items serve as roots to
 // start monomorphizing from.
 fn collect_roots(tcx: TyCtxt<'_>, mode: MonoItemCollectionMode) -> Vec<MonoItem<'_>> {
@@ -339,15 +334,7 @@ fn collect_roots(tcx: TyCtxt<'_>, mode: MonoItemCollectionMode) -> Vec<MonoItem<
 
         tcx.hir().krate().visit_all_item_likes(&mut visitor);
 
-        // When building an executable that starts from a main function, the monomorphizer will
-        // generate a function that wraps main and initializes rust "runtime" as well as handle
-        // the executable error code based on main's return value.
-        //
-        // For RMC, we don't need the start function, and we also can't handle it. Thus, skip
-        // this for now.
-        if !is_rmc(tcx) {
-            visitor.push_extra_entry_roots();
-        }
+        visitor.push_extra_entry_roots();
     }
 
     // We can only codegen items that are instantiable - items all of