Summary:
When saving the CCCS, we now correctly track the set of live registers and pass
them to the jump_SAVE_CCCS macro. This is now a variadic macro, but variadic
macros are supported by GCC since 3.0 and by all versions of clang, so this
should not be a problem.

Test Plan:
./validate with the following build options:

```
BuildFlavour = quick-llvm
SRC_HC_OPTS_STAGE1 = -fllvm-fill-undef-with-garbage
```

Reviewers: bgamari, simonmar, austin, rwbarton, simonpj

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1864

GHC Trac Issues: #11487