[ADT] Work around `enumerate` compilation error with modules enabled

This manifests on Apple clang 14 with `-DLLVM_ENABLE_MODULES=1` and
`-DLLVM_ENABLE_ASSERTIONS=1` and seems like a host compiler bug.

Sample compilation failure:
https://green.lab.llvm.org/green/view/LLDB/job/lldb-cmake/52513/consoleFull#-458239162a1ca8a51-895e-46c6-af87-ce24fa4cd561.

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D146340