Adding a new thread model to GCC

[i.nixman@autistici.org]

hi Eric, Jonathan,

I was able to successfully build gcc-trunk using the provided patch.
moreover, I was able to successfully build all of the packages used in 
the toolchain!
(gmp, mpfr, mpc, isl, libgnurx, bzip2, termcap, libffi, expat, ncurses, 
readline, gdbm, tcl, tk, openssl, xz-utils, sqlite, python3, binutils, 
gdb, make)

at first glance everything seems to be working as before!
I posted the information about this and the link to the archive on the 
project page: https://github.com/niXman/mingw-builds/issues/622



best!