checkpatch: add warning for lines starting with a '#' in commit log

Commit log lines starting with '#' are dropped by git as comments.
Add a check to emit a warning for these lines.

Also add a --fix option to insert a space before the leading '#' in
such lines.

Link: https://lkml.kernel.org/r/20201202205740.127986-1-dwaipayanray1@gmail.com
Signed-off-by: Dwaipayan Ray <dwaipayanray1@gmail.com>
Suggested-by: Joe Perches <joe@perches.com>
Suggested-by: Peilin Ye <yepeilin.cs@gmail.com>
Tested-by: Peilin Ye <yepeilin.cs@gmail.com>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -3033,6 +3033,15 @@ sub process {
 			$commit_log_possible_stack_dump = 0;
 		}
 
+# Check for lines starting with a #
+		if ($in_commit_log && $line =~ /^#/) {
+			if (WARN("COMMIT_COMMENT_SYMBOL",
+				 "Commit log lines starting with '#' are dropped by git as comments\n" . $herecurr) &&
+			    $fix) {
+				$fixed[$fixlinenr] =~ s/^/ /;
+			}
+		}
+
 # Check for git id commit length and improperly formed commit descriptions
 		if ($in_commit_log && !$commit_log_possible_stack_dump &&
 		    $line !~ /^\s*(?:Link|Patchwork|http|https|BugLink|base-commit):/i &&