[9fans] comment and newline in define

[lucio]

In /sys/src/cmd/cc/macbody:298,301

        if(c == '\n') {
                yyerror("comment and newline in define: %s", s->name);
                break;
        }

suggests that all "C" compilers explictly forbid newlines within
comments when a macro is #defined.  At a glance, I'd say that removing
the above will eliminate what to me seems an anachronism.  Am I
overlooking something?

The Go toolchain code unsurprisingly uses multiline comments in
src/cmd/ld/elf.h and I'm loath to request the Go Authors to hack their
header file for a non-standard feature of the Plan 9 compilers.  I
concede that the header in question would benefit, aesthetically, from
having those comments adjusted.

++L