Revert "[Refactor] Cleanup runtime code generation"

This reverts commit 215466 (and 215528, a trivial formatting fix).

The intention of these commits is a good one, but unfortunately they broke
our LNT buildbot:

http://lab.llvm.org:8011/builders/perf-x86_64-penryn-O3-polly-codegen-isl

Several of the cleanup changes that have been combined in this 'fixup' are
trivial and could probably be committed as obvious changes without risking to
break the build. The remaining changes are little and it should be easy to
figure out what went wrong.