Add a new subtarget hook for whether or not we'd like to enable

Add a new subtarget hook for whether or not we'd like to enable
the atomic load linked expander pass to run for a particular
subtarget. This requires a check of the subtarget and so save
the TargetMachine rather than only TargetLoweringInfo and update
all callers.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211314 91177308-0d34-0410-b5e6-96231b3b80d8