This patch simplifies genmultilib.awk so that it generates
MULTILIB_REQUIRED instead of the complement, MULTILIB_EXCEPTIONS.

The current awk script dates back to the days when we mapped
all the > 200 devices to the mmcu core and also parts of
--help=target to list all devices were generated from avr-mmcus.
That code rot is also cleaned up.  Moreover, the structure now allows
for simpler addition of new multilib options which are likely to come
in the near future.

The result of -print-multi-lib is:

.;
avr25;@mmcu=avr25
avr3;@mmcu=avr3
avr31;@mmcu=avr31
avr35;@mmcu=avr35
avr4;@mmcu=avr4
avr5;@mmcu=avr5
avr51;@mmcu=avr51
avr6;@mmcu=avr6
avrxmega2;@mmcu=avrxmega2
avrxmega4;@mmcu=avrxmega4
avrxmega5;@mmcu=avrxmega5
avrxmega6;@mmcu=avrxmega6
avrxmega7;@mmcu=avrxmega7
avrtiny;@mmcu=avrtiny
tiny-stack;@msp8
avr25/tiny-stack;@mmcu=avr25@msp8

hence unchanged.

Ok for trunk?

Johann


	* config/avr/t-avr (AWK) [t-multilib]: Remove "-v FORMAT=Makefile"
	command option from $(AWK) call.
	* config/avr/genmultilib.awk: Simplify and rewrite so that it
	generates MULTILIB_REQUIRED instead of MULTILIB_EXCEPTIONS.
	[FORMAT]: Remove handling of variable.
	* config/avr/t-multilib: Regenerate.