This adds a --enable-systemtap configure option, which will then
add static tracepoints to the generated libosmocore binary.
At this point, only two tracepoints are supported: log_start
and log_done. They can be used to trace the amount of time
a libosmocore-using application spends in potentiall blocking calls to
log to stderr or to files.
Related: OS#4311
Change-Id: I7e1ab664241deb524c9582cbd1bec31af46c747e
