[PING^1][patch][avr] New option -nodevicespecs to omit -specs=... in self specs.

[Georg-Johann Lay]

Ping #1

> Hi, currently device support in avr-gcc is accomplished by injecting a 
> specs file my means of -specs=... in dirver self specs.
> 
> This patch adds a new avr driver option to omit the addition of 
> respective -specs option so give the user more freedom.
> 
> Ok to apply?
> 
> Johann
> 
>     * config/avr/avr.opt (-nodevicespecs): New driver option.
>     * config/avr/driver-avr.c (avr_devicespecs_file): Only issue
>     "-specs=device-specs/..." if that option is not set.
>     * doc/invoke.texi (AVR Options) <-nodevicespecs>: Document.
>