IGEN - Replace IMEM (IMEM_IMMED) macro with IMEM<insn-size> macro,

IGEN - Replace IMEM (IMEM_IMMED) macro with IMEM<insn-size> macro,
update v850, tic80 and mips simulators.
IGEN - Prepend prefix to more generated symbols and macros
(idecode_issue, instruction_word).
IGEN - Add -Wnowith option to supress warnings about word size
inflicts in input files.
MIPS - Clean up Makefile.in, m16.igen, m16.dc (new), m16run.c (new) so
that a mips16 simulator built using IGEN can be compiled.