* Be less strict about multi-line preprocessor directives (e.g. those
with comments hanging off the right-hand end) since they're more
of a problem in practise than I expected. Prompted by phk.
* Fix the handling of "ignore" symbols.
* Style pedantry from OpenBSD and Ted Unangst <tedu@stanford.edu>,
including some whitespace fixes and removal of strcpy()
(and not including excessively strict KNF enforcement).
* Fix some typos and terminological inconsistencies.
* It now knows about the existence of #elif which would have
caused it to produce incorrect results in some situations.
* It can now process #if and #elif lines according to the
values of symbols that are specified on the command line.
The expression parser is only a simple subset of what C
allows but it should be sufficient for most real-world
code (it can cope with everything it finds in xterm).
* It has an option for printing all of the symbols that might
control #if processing. The unifdefall script uses this
option along with cpp -dM to strip all #ifs from a file.
* It has much larger static limits.
* It handles nested #ifs much more completely.
There have also been many style improvements: KNF; ANSI function
definitions; all global stuff moved to the top of the file; use
stdbool instead of h0h0bool; const-correctness; err(3) instead
of fprintf(stderr, ...); enum instead of #define; commentary.
I used NetBSD's unifdef as the basis of this since it has received
the most attention over the years.
PR: 37454
Reviewed by: markm, dwmalone
Approved by: dwmalone (mentor)
MFC after: 3 weeks
