ManagedStatic: remove many straightforward uses in llvm

(Reapply after revert in e9ce1a58 due to
Fuchsia test failures. Removed changes in lib/ExecutionEngine/ other
than error categories, to be checked in more detail and reapplied
separately.)

Bulk remove many of the more trivial uses of ManagedStatic in the llvm
directory, either by defining a new getter function or, in many cases,
moving the static variable directly into the only function that uses it.

Differential Revision: https://reviews.llvm.org/D129120