compiler: don't export any functions with special names

This keeps init functions from appearing in the export data.  Checking
    for special names in general means that we don't need to check
    specifically for nested functions or thunks, which have special names.
    
    Reviewed-on: https://go-review.googlesource.com/c/143237

From-SVN: r265321

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-6f4bce815786ff3803741355f7f280e4e2c89668
+e1dc92a6037a3f81ea1b8ea8fb6207af33505f0c
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/export.cc

@@ -75,12 +75,8 @@ should_export(Named_object* no)
   if (Gogo::is_hidden_name(no->name()))
     return false;
 
-  // We don't export nested functions.
-  if (no->is_function() && no->func_value()->enclosing() != NULL)
-    return false;
-
-  // We don't export thunks.
-  if (no->is_function() && Gogo::is_thunk(no))
+  // We don't export various special functions.
+  if (Gogo::is_special_name(no->name()))
     return false;
 
   // Methods are exported with the type, not here.