Use relatives jumps

[vaivaswatha]

Description

Switch the compiler to use relative jumps instead of absolute jumps.

1. The function relocate_control_flow is now removed. It used to move basic blocks around in case absolute addresses crossed the easily addressable boundary. The code movement can then avoid having to load the address to a register and using indirect jumps. This is unlikely to happen with relative jumps. But if it does, the existing algorithm wouldn't work anyway. So we can add a new one when required later.
2. In the case of function call jumps, we use $pc to save the return address for the callee. This is a bit inefficient as it involves 3 extra computations: $$reta = ($pc - $is) / 4 + offset_to_return_point. We could change this to the following: Since we already have a common return point for every function, compute the relative offset from that point to the callee return point statically and use that. We don't have the infrastructure to do that right now, but it shouldn't be too difficult an extension.

Fixes #4443