Hello,

C Mode autoindents CWEB style lines undesirably.

Steps to reproduce
  . starting from 'emacs -Q'
  . open new file 'C-x f /dev/shm/explain.w'
  . enable mode for C 'M-x c-mode'
  . enter the C CWEB style source text below
  . Explanation}
      the last two lines autoindent but I expect them to be without
  . at line 6 below at # position c-set-offset reports 'cpp-macro'
  . at line 0 below at # position c-set-offset reports 'cpp-macro'

Expected result is for lines 6, F and 0 below to be without indent.

```
1 @** Convert 511 decimal to octal.
2 @d _x_number_x_ 511
3 @d _x_banner_x_ "What is the value of %d in octal?"
4 @c
5 #include <stdio.h>
6 #include "u.h"
7 int@/
8 main(void)@/
9 {
A   int n = _x_number_x_;
B   printf (_x_banner_x_, n);
C   printf ("%s! %d decimal is %o octal\n", "Right", n, n);
D }
E @ @(u.h@>=
F     @h
0     #include <stdlib.h>
```

-- 
vl