PR18501: Add tapset support and test coverage for the kcmp syscall

PR18501: Add tapset support and test coverage for the kcmp syscall

* tapset/linux/aux_syscalls.stp: New function _kcmp_type_str()
* tapset/linux/nd_syscalls.stp: New probe nd_syscall.kcmp
* tapset/linux/syscalls.stp: New probe syscall.kcmp
* testsuite/buildok/aux_syscalls-embedded.stp: New subtest
* testsuite/buildok/nd_syscalls-detailed.stp: Ditto
* testsuite/buildok/syscalls-detailed.stp: Ditto
* testsuite/systemtap.syscall/kcmp.c: New testcase