Compile with C++17 (compatibility with abseil)

[h-vetinari]

I hit a problem in conda-forge/or-tools-feedstock#21, which is that:

cannot convert 'sp' (type 'absl::lts_20220623::string_view*' {aka 'std::basic_string_view<char>*'}) to type 're2::StringPiece*'

The situation is described in more detail in this upstream commit google/re2@6543c37, but I don't think we want to consider building the upstream abseil branch.

The respective header switches on #ifdef __cpp_lib_string_view, so it should work fine once we compile it with C++17.

Note however that this will be an ABI change (intentionally, because as of now re2::StringPiece doesn't match std::string_view, but afterwards it would), so we'll have to figure out how to do this (e.g. we could bump the version from 2023-02-01 to 2023-02-02, but that would mean remigrating everything).

CC @conda-forge/re2

[h-vetinari]

Giving this a shot in #62