[RFA] Integrated hashtables take 2

[Neil Booth]

Zack Weinberg wrote:-

> If we un-box identifiers - make them something other than trees - this
> problem will go away.  I think it's reasonable to share the basic
> 'struct identifier' between cpplib and gcc.

I had a quick look into this, and I believe it's a lot harder than
you seem to think.

A lot of code assumes that the tree_common fields are there, even if
NULL, and treats IDENTIFIER_NODEs as trees.  Garbage collection, for a
start.

Neil.