[SimplifyCFG] put the optional assumption cache pointer in the options struct; NFCI

[SimplifyCFG] put the optional assumption cache pointer in the options struct; NFCI

This is a follow-up to https://reviews.llvm.org/D38138.

I fixed the capitalization of some functions because we're changing those
lines anyway and that helped verify that we weren't accidentally dropping
any options by using default param values.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314930 91177308-0d34-0410-b5e6-96231b3b80d8