PR18293: Test coverage improvements, tapset extension.

PR18293: Test coverage improvements, tapset extension.

* tapset/linux/aux_syscalls.stp: Add auxiliary functions for times and sysinfo.
* tapset/linux/nd_syscalls2.stp: Extend argstr for sysinfo and times.
* tapset/linux/syscalls2.stp: Likewise.
* testsuite/buildok/nd_syscalls2-detailed.stp: New convenience var for times syscall.
* testsuite/buildok/syscalls2-detailed.stp: Likewise for nd_syscall.times.
* testsuite/systemtap.syscall/clock.c: Addo coverage for stime syscall.
* testsuite/systemtap.syscall/syncfs.c: Extend and fix the testcase.
* testsuite/systemtap.syscall/sysctl.c: New testcase.
* testsuite/systemtap.syscall/sysinfo.c: Likewise.
* testsuite/systemtap.syscall/times.c: Likewise.
* testsuite/systemtap.syscall/unshare.c: Likewise.