checkpatch: Improve macros with flow control test

The current test excludes any macro with ## concatenation from being
reported with hidden flow control.

Some macros are used with return or goto statements along with ##args or ##__VA_ARGS__. A somewhat common case is a logging macro like pr_info(fmt, ...) then a return or goto statement.

Check the concatenated variable for args or __VA_ARGS__ and allow those macros to also be reported when they contain a return or goto.

---

index 2b3c228..76e4b33 100755
@@ -4517,7 +4517,7 @@ sub process {
 			#print "LINE<$lines[$ln-1]> len<" . length($lines[$ln-1]) . "\n";
 
 			$has_flow_statement = 1 if ($ctx =~ /\b(goto|return)\b/);
-			$has_arg_concat = 1 if ($ctx =~ /\#\#/);
+			$has_arg_concat = 1 if ($ctx =~ /\#\#/ && $ctx !~ /\#\#\s*(?:__VA_ARGS__|args)\b/);
 
 			$dstat =~ s/^.\s*\#\s*define\s+$Ident(?:\([^\)]*\))?\s*//;
 			$dstat =~ s/$;//g;