Changes

[MustExecute] Silence clang warning about unused captured 'this'
New code introduced in fe799c97fa caused clang to complain with
../lib/Analysis/MustExecute.cpp:360:34: error: lambda capture 'this' is
not used [-Werror,-Wunused-lambda-capture]
 GetterTy<LoopInfo> LIGetter = [this](const Function &F) {
                                ^~~~
../lib/Analysis/MustExecute.cpp:365:44: error: lambda capture 'this' is
not used [-Werror,-Wunused-lambda-capture]
 GetterTy<PostDominatorTree> PDTGetter = [this](const Function &F) {
                                          ^~~~ 2 errors generated.