cmake: introduce target checkpatch

The patch introduces a new CMake target "checkpatch", that checks
patches on top of the master branch using script checkpatch.pl [1]. By
default CMake looking for `checkpatch.pl` in a directory "checkpatch" in
Tarantool's repository root directory and in a directories specified in
PATH. By default commit revisions range checked by checkpatch is
`origin/master..HEAD`, `origin/master` could be overridden with
environment variable `CHECKPATCH_GIT_REF`.

1. https://github.com/tarantool/checkpatch

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