Portability: Early SGS and PCC compiler errors

[johnsonjh]

Example: Motorola SYSTEM V/68, Release 2, Version 1.0, VME/10 68010:

$ cc -c -O -DSYSV -DRUNOPTS -DUSEDIRENT ccpu.c
"ccpu.c", line 2142: compiler error: switch table overflow

Other systems using AT&T System V SGS compiler derivatives have the same trouble (e.g. Multics C).

On these compilers, the maximum switch table size is a preprocessor defintion set at compile time, so not trivial to patch.

Possible solutions (besides updating the compiler):

1. Add #ifdef to leave out undocumented instructions.
2. Convert switch/case to if/else.