This update for re2 fixes the following issues:

- Switch build to CMake, otherwise CMake config is not installed.
  Required for Apache ORC and arrow, and google-or-tools.
  (https://github.com/google/re2/issues/304)
- Run some real tests via CTest

Update to 2022-04-01:

* Improve performance slightly
* Prog::Fangout() is no longer experimental

Update to 2022-02-01:

* Address a `-Wunused-but-set-variable' warning from Clang 13.x
* Don't specify the -std flag in Makefile or re2.pc
* Remove a redundant map access