binutils: bring up to date in terms of home-brew formula style

* add sha for patch to ensure we’re applying the right changes
* build in a subdir
* change option naming to match homebrew convention
binutils: update to version 2.24
gcc: update to 4.8.3

also

* update option naming to match homebrew convention
* default homebrew environment is acceptable
* configure gcc to avoid installing libiberty
libc: update to 1.8.1

also

* only clear the portions of the environment that are required
* specify the prefix as the avr-gcc prefix so we don’t need to copy files separately afterwards
Pull #23