needless deep recursion in gt-c-decl.h

[Per Bothner]

Zack Weinberg wrote:
> This creates a hidden assumption which may not actually be true: that
> all RTL is reachable from the GC root set independent of pointers from
> tree nodes.

I don't know.  While I don't think the compiler currently does this,
it may be reasonable to use FUNCTION_DECLs as the "logical root" for
the INSNs created for the function.  In that case there should be a
single top-level pointer to the INSN-chain, and of course we must
follow it.

My point is about the various redundant cross- and back-references.
-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/per/