Improve the setup for ticky

Simon Marlow and I came up with the following proposals:

• Merge the "ticky" and "debug" builds of the runtime system. This just simplifies the RTS build, and reduces the number of versions.
• Arrange that every build of the RTS defines the symbols that are referenced by code compiled with -ticky. That way you won't get link errors if you compile tickified code with a non-debug RTS.

The second point is very important. When testing I often want to compile all the libraries with -ticky, but it's very fiddly to ensure that every program compiled against those libraries is linked against the debug/ticky RTS. I just want those programs to work. The ones I want to examine closely (ie see the ticky stats) I can certainly link with -ticky or -debug to get the RTS that does the counting.

None of this is difficult; just an hour or two's work.