Find alternative ways to get list of NANOTESTs

Right now cmake invokes a python code generator that generates a header which has pointers to the test functions. This is pretty painless in cmake builds, but not ideal.

Originally I used linkersets but the location of the structs in the linker section aren't guaranteed to be contiguous. Clang with -fsanitize=address blows up as it adds redzones. Also, alignment is a problem if the structs aren't properly sized.

I'm sure there is some other linker magic that can be leveraged to use this and remove the dependency on python or (error prone) manual header generation.