ARM: Convert fork.c to arch-fork.h
PowerPC: clean BSD Terminal Modes expectation in termios.h

This patch guard the BSD definition for terminal modes in PowerPC
specific header fixing the following conformance failures:

FAIL: conform/POSIX/termios.h/conform
FAIL: conform/POSIX2008/termios.h/conform
FAIL: conform/UNIX98/termios.h/conform