checkpatch: Handle long multi-line macros better.

Improve parsing of multiline macros which run beyond the available
diff context.  These beyond-the-horizon macros previously caused
two distinct naughty behaviors:
  - The scanner, confused by the trailing backslash, would grab
    the header of the next context hunk and treat it as the last
    line of the preceding macro.
  - The analyzer, unable to fully reduce the macro, would blame
    the patch for submitting an unbalanced or unprotected macro.

Change-Id: I6b7dd3d577c524d30b59dff7b20393bb5135f16d
Signed-off-by: Gregory Bean <gbean@codeaurora.org>
(cherry picked from commit ddd028c47b4d91aa9c0e97445eb584b2de367769)
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>

scripts/checkpatch.pl

@@ -4923,7 +4923,7 @@ sub process {
 		if ($realfile !~ m@/vmlinux.lds.h$@ &&
 		    $line =~ /^.\s*\#\s*define\s*$Ident(\()?/) {
 			my $ln = $linenr;
-			my $cnt = $realcnt;
+			my $cnt = $realcnt - 1;
 			my ($off, $dstat, $dcond, $rest);
 			my $ctx = '';
 			my $has_flow_statement = 0;
@@ -4960,6 +4960,12 @@ sub process {
 			{
 			}
 
+			# Extremely long macros may fall off the end of the
+			# available context without closing.  Give a dangling
+			# backslash the benefit of the doubt and allow it
+			# to gobble any hanging open-parens.
+			$dstat =~ s/\(.+\\$/1/;
+
 			# Flatten any obvious string concatentation.
 			while ($dstat =~ s/($String)\s*$Ident/$1/ ||
 			       $dstat =~ s/$Ident\s*($String)/$1/)