bug#50331: 28.0.50; Propose to obsolete cwarn.el

[Zhiwei Chen <condy0919@gmail.com>]

Today, modern compilers can recognize the three cases described in cwarn file.

# semicolon after if/for/while

if (value);
  foo();

g++ -Wall produces helpful diagnostic information:

a.cpp:11:5: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘if’
   11 |     foo();
      |     ^~~


# assignment in expression

if (x = 0)
  foo();

a.cpp:10:9: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   10 |   if (x = 0);
      |       ~~^~~

g++ -Wall does a great job.


# reference parameter uses

int bar(int& a) {
  return a;
}

I don't think it should be displayed in warning face, it's widely used today.

# conclusion

Since the first two cases are not existent, and the last one is false
positive (IMO), I propose to obsolete cwarn.

CCed Anders Lindgren, the author of cwarn.

-- 
Zhiwei Chen