Use X86 memory operand enums instead of hardcoding.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208064 91177308-0d34-0410-b5e6-96231b3b80d8
Update programmers manual to cover llvm::function_ref, and add a note to the
coding standard suggesting using it instead of the (unavailable) std::function.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208067 91177308-0d34-0410-b5e6-96231b3b80d8