gcc: update to allow compiling different versions

This is based on the toolchain GCC, and aims to share as much of its
Makefile and patches with that definition. The package requires two
additional patches:

(1) 003-dont-choke-when-building-32bit-on-64bit.patch, which fixes the
`error: size of array 'test_real_width' is negative` error that occurs
when building a 32-bit GCC on a 64-bit host. (Search the Internet for
examples of this error appearing.)

(2) 980-add-nostdinc++.patch, which backports a fix from 11.3.0 (11.2.0
only).

Signed-off-by: W. Michael Petullo <mike@flyn.org>