[clang-tidy] fix PR36489 - respect deduced pointer types from auto as well

Summary:
The cppcoreguidelines-pro-bounds-pointer-arithmetic warns on all occassion where
pointer arithmetic is used, but does not check values where the pointer types
is deduced via `auto`. This patch adjusts this behaviour and solved
PR36489.
I accidentally commited a wrong patch, this Differential is meant to have a
correct revision description and code attached to it.
Because the patch was accepted by aaron.ballman already, i will just commit
it.
See https://reviews.llvm.org/D48717 for the old differntial (contains wrong
code from the mixup)

Subscribers: nemanjai, xazax.hun, kbarton, cfe-commits

Differential Revision: https://reviews.llvm.org/D49682

llvm-svn: 337716