Darwin, crts: Build Darwin10 unwinder shim as a library.

Darwin, crts: Build Darwin10 unwinder shim as a library.

We have a small unwinder shim that is only used for Darwin10
(and only then in quite specific cases).  To avoid linking
this code for every executable or DSO, we can present the crt
as a convenience library (rather than a .o file).

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
gcc/ChangeLog:

	* config/darwin.h (LINK_COMMAND_SPEC_A): Use Darwin10
	unwinder shim as a convenience library.

libgcc/ChangeLog:

	* config.host: Use convenience library for Darwin10
	unwinder shim.
	* config/t-darwin: Build Darwin10 unwinder shim as a
	convenience library.

(cherry picked from commit 873854387865d18484bd0d39324773cd1e76df85)