[Simplify] Fix r302986 that introduced non-inferrable templates.

- auto + decltype + template use was not inferrable in
  `Transform/Simplify.cpp accessesInOrder`.

- changed code to explicitly construct required vector instead of using
  higher order iterator helpers.

- Failing compiler spec:
    Apple LLVM version 7.3.0 (clang-703.0.31)
    Target: x86_64-apple-darwin15.6.0

llvm-svn: 303039