checkpatch: Escape range operators inside regex.

' -(' matches a single character in the range between ' ' (index 32)
and '(' (index 40). This leads to the false positive:

  WARNING: Line lacks whitespace around operator
  #445 FILE: ovsdb/monitor.c:573:
      if (--mcs->n_refs == 0) {

Need to escape '-' to have a right behaviour.
This patch additionally escapes all other '-' chars in the similar
regexes and makes them be one per line to ease the review in case of
future changes.

Basic unit tests added.

CC: Joe Stringer <joe@ovn.org>
Fixes: 0d7b16daea ("checkpatch: Check for infix operator whitespace.")
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

utilities/checkpatch.py

@@ -612,9 +612,14 @@ infix_operators = \
     [re.escape(op) for op in ['%', '<<', '>>', '<=', '>=', '==', '!=',
             '^', '|', '&&', '||', '?:', '=', '+=', '-=', '*=', '/=', '%=',
             '&=', '^=', '|=', '<<=', '>>=']] \
-    + ['[^<" ]<[^=" ]', '[^->" ]>[^=" ]', r'[^ !()/"]\*[^/]', '[^ !&()"]&',
-       r'[^" +(]\+[^"+;]', '[^" -(]-[^"->;]', r'[^" <>=!^|+\-*/%&]=[^"=]',
-       '[^* ]/[^* ]']
+    + [r'[^<" ]<[^=" ]',
+       r'[^\->" ]>[^=" ]',
+       r'[^ !()/"]\*[^/]',
+       r'[^ !&()"]&',
+       r'[^" +(]\+[^"+;]',
+       r'[^" \-(]\-[^"\->;]',
+       r'[^" <>=!^|+\-*/%&]=[^"=]',
+       r'[^* ]/[^* ]']
 checks += [
     {'regex': r'(\.c|\.h)(\.in)?$', 'match_name': None,
      'prereq': lambda x: not is_comment_line(x),