[Patch,avr] Document __AVR_ARCH__

[Weddington, Eric]

> -----Original Message-----
> From: Georg-Johann Lay 
> Sent: Thursday, October 18, 2012 5:08 AM
> To: gcc-patches@gcc.gnu.org
> Cc: Denis Chertykov; Weddington, Eric
> Subject: [Patch,avr] Document __AVR_ARCH__
> 
> This documents __AVR_ARCH__ built-in macro that was missing up to now.
> 
> Pointer to --help=target is removed because the documentation of -mmcu= is
> complete.
> 
> Ok to apply?
> 

Approved, please apply! And Thanks!

Eric