This is the handwritten part of the patch; automated part to follow.
* cgraph.h (symtab_node_base): Convert to a class;
add GTY((desc ("%h.type"), tag ("SYMTAB_SYMBOL"))), and take
chain_next/prev from symtab_node_def.
(cgraph_node): Inherit from symtab_node; add GTY option
tag ("SYMTAB_FUNCTION").
(varpool_node): Inherit from symtab_node; add GTY option
tag ("SYMTAB_VARIABLE").
(symtab_node_def): Remove.
(is_a_helper <cgraph_node>::test (symtab_node_def *)): Convert to...
(is_a_helper <cgraph_node>::test (symtab_node_base *)): ...this.
(is_a_helper <varpool_node>::test (symtab_node_def *)): Convert to...
(is_a_helper <varpool_node>::test (symtab_node_base *)): ...this.
* ipa-ref.h (symtab_node_def): Drop.
(symtab_node): Change underlying type from symtab_node_def to
symtab_node_base.
(const_symtab_node): Likwise.
* is-a.h: Update examples in comment.
* symtab.c (symtab_hash): Change symtab_node_def to symtab_node_base.
(assembler_name_hash): Likewise.
From-SVN: r204170
