Smaller C fixes and improvements

- move va_list type detection under #ifdef as it's rarely needed anyway
- allow up to 254 characters in a string literal
- generate a warning when an integer is passed instead of a pointer (and
vice versa) as a function parameter (pass -Wall for this)
- when printing an unexpected token, print identifier tokens instead of
'\<tokIdent\>'
- fix: allow most control characters inside '' and ""
- fix handling of -I\<path\> and -SI\<path\>
- switch() now supports Duff's device
- for() now supports declarations in its first clause as in C99/C++
- reduce smlrc size on RetroBSD by making most functions static if macro STATIC is defined
- make share/smallc/hello.c compilable with Small C again (make in share/smallc should now just work)