Don't emit shared libraries

[vchuravy]

Currently there is a technical limitation on how we can emit probes.
Originally my plan was to just inline assembly to generate the nop and the note,
but none of bcc/bptrace tools could find the notes and therefore the probes.

As an example tplist scans /proc/pid/maps for files and then scans each file to read the notes from there. Since Julia objectfiles are not mapped as pseudo-elf (check GDB integration for how we notify GDB about new objectfiles) none of these tools could discover them. Furthermore we do need a linker step to make the notes valid...

So for now we have to live with the fact that we have to do a ccall to a nop instead of having just a nop ...