uselistorder: Thread bit through ValueEnumerator

Canonicalize access to whether to preserve use-list order in bitcode on
a `bool` stored in `ValueEnumerator`.  Next step, expose this as a
`bool` through `WriteBitcodeToFile()`.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234956 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed