initial support for static userspace probes via systemtap

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
diff --git a/src/probes.d b/src/probes.d
new file mode 100644
index 0000000..c16eb1e
--- /dev/null
+++ b/src/probes.d
@@ -0,0 +1,4 @@
+provider libosmocore {
+	probe log_start();
+	probe log_done();
+};