C++ build tries to build systemtap (DTrace compatible) probes where they won't work

Currently Qpid's use of systemtap static probes will only compile and work on Linux even though the probe syntax should be compatible with FreeBSD and Solaris. This is because of differences in implementation and tools.

It would be better if the build only tried to build probes on Linux systems by default. This will avoid inscrutable link errors when building on other systems with the necessary header files, that make it seem that qpid is unbuildable.