Support installing headers for bootstrapping libgcc

[Joseph S. Myers]

On Mon, 14 May 2012, Joseph S. Myers wrote:

> For IA64, I don't know what issues may arise, and IA64 testing will be 
> important for later patch revisions.

I should add: the concern for IA64 is really only not to break it, rather 
than to make bootstrap builds work there; IA64 has never had the support 
in GCC for the sort of bootstrap builds I hope to make easier 
(specifically, other architectures have inhibit_libc conditionals on 
architecture-specific bits of libgcc using system headers; IA64 doesn't), 
so I'm not particularly concerned about failing to make bootstraps 
smoother for IA64 if they can be made smoother for all other platforms.

-- 
Joseph S. Myers
joseph@codesourcery.com