Don't assume that iterators can be compared.

std::string_view in MSVC has iterators that aren't just pointers and
that don't allow comparisons between different objects - not even if
those objects are views into the same string!

Change-Id: I0b61ca4a42bcbb9eda85df47c5f233dbf488e107
Reviewed-on: https://code-review.googlesource.com/c/re2/+/59330
Reviewed-by: Julien Goodwin <julieng@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>
9 files changed