#57 add support for -el option: like -e, but without %LINE

[nasm64developer]

Attached is a diff against nasm.c 0.98.38, which
adds support for the -el option. It's identical
to the existing -e option, except that it doesn't
emit any %LINE directives.

This functionality can come in handy when one is
trying to analyze code with the help of both, the
-e and the -a option.

In my particular case -e emitted %LINE directives
with a line increment of zero... which of course
made it difficult to trace error messages emitted
by the subsequent -a run.

Also, the -el option brings us one step closer to
being able to use NASM's preprocessor to operate
on files that don't contain assembly source code.

It seems as if the only missing piece is support
for maintaining TOK_COMMENT tokens throughout the
preproc.c code, without breaking anything.

[nasm64developer]