* Add missing include for VxWorks build.

std::min is defined in algorithm provides std::min. It appears to be transitively included for most platforms. For VxWorks however this explicit include is required.

* Add option CATCH_CONFIG_PREFIX_MESSAGES to selectively prefix message macros only.

In contrast to CATCH_CONFIG_PREFIX_ALL, this will only prefix the following macros:
I.e. INFO, UNSCOPED_INFO, WARN and CATCH_CAPTURE

This is mainly useful for codebases that use INFO or WARN for their own logging macros.

* Add new `CATCH_CONFIG` option for using `std::getenv`, because PS does not support env vars
* Add PS to platforms that have disabled posix signals.
* Small workaround for PS toolchain bug that prevents it from compiling `std::set` with lambda based comparator.