Use libgcc instead of providing needed "builtin" functions for GCC
An initial design guideline for the kernel was to depend on no external code, and this is why the kernel is not linked with libgcc. As GCC expects its output to be linked with its runtime library, it may emit implicit calls to some functions provided by libgcc, like udivsi4_xxx, and several memcpy/movmem like functions.
Right now, these needed functions are added when necessary, in gcc_fix and utils/sh directories. Some reasons to avoid that are given in OSDev wiki. As FiXos depends on GCC for many other features, I think its time to remove this old behavior, and to depends on libgcc features.