[debug-early] make gen_typedef_die gracefully handle error marks

[Aldy Hernandez]

Now that we call dwarf2out earlier in the compilation process, we may 
get some error_mark_node's.  And of course, nobody likes an ICE...

Committed to branch.
commit 92437112d3d4966eecb31df59a6fa4a1014a198c
Author: Aldy Hernandez <al...@redhat.com>
Date:   Fri Apr 24 14:24:09 2015 -0700
    Make gen_typedef_die handle a type of error_mark_node.

diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index 39046f5..11bbade 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -20617,6 +20617,9 @@ gen_typedef_die (tree decl, dw_die_ref context_die)
        {
          type = DECL_ORIGINAL_TYPE (decl);
 
+         if (type == error_mark_node)
+           return;
+
          gcc_assert (type != TREE_TYPE (decl));
          equate_type_number_to_die (TREE_TYPE (decl), type_die);
        }
@@ -20624,6 +20627,9 @@ gen_typedef_die (tree decl, dw_die_ref context_die)
        {
          type = TREE_TYPE (decl);
 
+         if (type == error_mark_node)
+           return;
+
          if (is_naming_typedef_decl (TYPE_NAME (type)))
            {
              /* Here, we are in the case of decl being a typedef naming