Added dtrace testcases for clone, fork/exec, and vfork/exec.
* testsuite/systemtap.clone/Makefile.clone: New file.
* testsuite/systemtap.clone/Makefile.fork_exec: Ditto.
* testsuite/systemtap.clone/Makefile.vfork_exec: Ditto.
* testsuite/systemtap.clone/dtrace_child.c: Ditto.
* testsuite/systemtap.clone/dtrace_child_probes.d: Ditto.
* testsuite/systemtap.clone/dtrace_clone.c: Ditto.
* testsuite/systemtap.clone/dtrace_clone.exp: Ditto.
* testsuite/systemtap.clone/dtrace_clone.stp: Ditto.
* testsuite/systemtap.clone/dtrace_clone_probes.d: Ditto.
* testsuite/systemtap.clone/dtrace_fork_exec.exp: Ditto.
* testsuite/systemtap.clone/dtrace_fork_exec.stp: Ditto.
* testsuite/systemtap.clone/dtrace_fork_parent.c: Ditto.
* testsuite/systemtap.clone/dtrace_fork_parent_probes.d: Ditto.
* testsuite/systemtap.clone/dtrace_vfork_exec.exp: Ditto.
* testsuite/systemtap.clone/dtrace_vfork_exec.stp: Ditto.
* testsuite/systemtap.clone/dtrace_vfork_parent.c: Ditto.
* testsuite/systemtap.clone/dtrace_vfork_parent_probes.d: Ditto.
* testsuite/systemtap.clone/test_progs.tcl: Ditto.