checkpatch: fix macro argument reuse test

Multiple line macro definitions where the arguments are separated by line
continuations can cause checkpatch to emit invalid syntax regex tests.

This can occur when a single argument is modified in a part of a patch.

For example: (to not add a diff in the commit message)

$ ./scripts/checkpatch.pl --git db023296f0
Unterminated \g... pattern in regex; <very long regex omitted>

And, the test does not work correctly when these arguments are all new as
the initial patch line addition "+" is used in the argument name.

Fix this by stripping the line continuations and any "+" from the list of
arguments.

Link: http://lkml.kernel.org/r/86cdb43a4db70670c102020093f7fb4eb3003e01.camel@perches.com
Signed-off-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

@@ -4967,6 +4967,7 @@ sub process {
 			if (defined $define_args && $define_args ne "") {
 				$define_args = substr($define_args, 1, length($define_args) - 2);
 				$define_args =~ s/\s*//g;
+				$define_args =~ s/\\\+?//g;
 				@def_args = split(",", $define_args);
 			}