add coccicheck make target

add coccicheck make target

Provide a simple way to run Coccinelle against all source files, in the
form of a Makefile target.  Running "make coccicheck" applies each
.cocci file in contrib/coccinelle/ on all source files.  It generates
a .patch file for each .cocci file, containing the actual changes for
effecting the transformations described by the semantic patches.

Non-empty .patch files are reported.  They can be applied to the work
tree using "patch -p0", but should be checked to e.g. make sure they
don't screw up formatting or create circular references.

Coccinelle's diagnostic output (stderr) is piped into .log files.

Linux has a much more elaborate make target of the same name; let's
start nice and easy.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>