[FR] Support RE2 regular expression engine

[ricea]

Is your feature request related to a problem? Please describe.
When given an invalid regular expression, Chromium perftests using this library crash.

This is because Chromium compiles google_benchmark with std::regex and with exceptions disabled, and so there's no way for it to recover from a regular expression parsing error.

Describe the solution you'd like
When given an invalid regular expression, an error should be reported and no benchmarks should be run.

The Chromium project already incorporates the re2 regular expression library, so if it was possible for the embedder to provide the re2 engine then this problem could be solved.

Describe alternatives you've considered
Chromium could use the POSIX regex library, but it wouldn't work on Windows. Chromium could use the POSIX regex library on non-Windows platforms, but then behaviour would differ between platforms, which causes a lot of problems.

Additional context
N/A