Michal Terepeta authored Jul 28, 2017 and Ben Gamari committed Jul 28, 2017

This is another change needed for #13825 (also based on D38 by Simon
Marlow).

With the change, we count the stack depth in bytes (instead of words).
We also introduce some `newtype`s to help with the change.

Note that this only changes how `ByteCodeGen` works and shouldn't
affect the generated bytecode.

Signed-off-by: Michal Terepeta <michal.terepeta@gmail.com>

Test Plan: ./validate

Reviewers: bgamari, simonmar, austin, hvr

Reviewed By: bgamari, simonmar

Subscribers: rwbarton, thomie

GHC Trac Issues: #13825

Differential Revision: https://phabricator.haskell.org/D3746