devel/libphonenumber: update to 8.12.41, latest upstream

This update introduces new tools, which use abseil. The build
system tries to git-clone the abseil repo and build that.
Instead, use devel/abseil. However, devel/abseil is built as
C++17, so we need to patch the build to force C++17 on
libphonenumber as well (otherwise, abseil introduces pre-C++17
versions of string_view and link failures follow).

We set WRKSRC_SUBDIR, but the build system now *also*
goes off to ../tools/cpp (from that SUBDIR), so .. I suppose
we could drop the SUBDIR setting and instead try some other
way of invoking CMake for only the C++ parts. Rather than doing
that, keep SUBDIR, but that gives us a patch with path ../tools/
which deservers mention. Consider it mentioned.