PR23285 (1): enable procfs probes for stapbpf

PR23285 (1): enable procfs probes for stapbpf

The eBPF backend now supports procfs probes. This implementation
uses FIFO special files instead of proc filesystem files. The file
path format used is /var/tmp/systemtap-USER/MODNAME. One limitation
is that both read and write probes cannot exist for the same file.

1) Added procfs probe data structures to hold probe information.
2) Created an interface between target variables and eBPF interpreter.
3) Dedicated a single thread for each file which monitors for I/O.
4) Developed a cleaning routine and error handling mechanisms.
5) Updated NEWS and man pages.

small fix

new procfs_bpf test