Add warn(unreachable_pub) to rustc_expand.

Plus a tiny bit of reformatting.

compiler/rustc_expand/src/proc_macro_server.rs

@@ -414,7 +414,7 @@ impl ToInternal<rustc_errors::Level> for Level {
     }
 }
 
-pub struct FreeFunctions;
+pub(crate) struct FreeFunctions;
 
 pub(crate) struct Rustc<'a, 'b> {
     ecx: &'a mut ExtCtxt<'b>,
@@ -426,7 +426,7 @@ pub(crate) struct Rustc<'a, 'b> {
 }
 
 impl<'a, 'b> Rustc<'a, 'b> {
-    pub fn new(ecx: &'a mut ExtCtxt<'b>) -> Self {
+    pub(crate) fn new(ecx: &'a mut ExtCtxt<'b>) -> Self {
         let expn_data = ecx.current_expansion.id.expn_data();
         Rustc {
             def_site: ecx.with_def_site_ctxt(expn_data.def_site),