This commit adds support for the avr-libc C library.
According to the project page at http://www.nongnu.org/avr-libc , the
avr-libc package provides a subset of the standard C library for Atmel
AVR 8-bit RISC microcontrollers. In addition, the library provides the
basic startup code needed by most applications.
Support for this library in crosstool-ng is only enabled for the AVR
8-bit target.
The avr-libc manual and most distributions build the AVR 8-bit gcc
toolchain with the "avr" (non-canonical) target.
Some experimentation also led to the conclusion that other (canonical)
targets are not very well supported, so we force the "avr" target for
crosstool-ng as well.
The manual also recommends building avr-libc after the final gcc build.
To accomplish this with crosstool-ng, a new do_libc_post_cc step is
added, in which currently only avr-libc performs its build, and is a
no-op for the other libc options.
Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
