[clang-tidy] Rewrite a for-range loop in the old style.

Haven't thought that I ever needed to do this, but in this case comparing the
index using pointer arithmetic turns out to be really ugly. It also generates
nasty sign-compare warnings on 32 bit targets.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@214705 91177308-0d34-0410-b5e6-96231b3b80d8