build: Support sysprof-6
Sysprof 45 changed the API version of the main library. We mainly depend on sysprof-capture which is not affected, except for looking up the datadir where sysprof's D-Bus interfaces are installed.
That lookup doesn't care whether we are using sysprof-6 or sysprof-4, so accept either dependency.
I'll leave figuring out the sysprof wrap to !3142, but off-hand I don't see a reason why we shouldn't be able to build on systems where sysprof-4 is no longer available.
Fixes #2962 (closed)