[PATCH libgloss/arm] discourge the use of blx when it's not supported

[Bin Cheng]

> Hi Bin, Hi Carl,
> 
>    Sorry for the delay in reviewing this patch - I was on vacation.
> 
>    Anyway I have looked over the patch, and it is fine.  I have checked
> it in, along with a slightly expanded changelog entry:
> 
> Cheers
>    Nick
> 
> libgloss/ChangeLog
> 2011-09-29  Bin Cheng  <bin.cheng@arm.com>
> 
> 	* arm/arm.h (HAVE_CALL_INDIRECT): Define.
>          * arm/crt0.S (indirect_call): New macro.  Encodes indirect
> 	function calls.  Does not use blx for pre-armv5 targets.

Thanks very much, Nick.