* 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.

The license file was renamed with 6a502cc2f5fedd59b3495b58708f0d6d987ed9e1

With the changes to how `-ffile-prefix-map` is detected, Catch2 started propagating the flag to its dependents, which isn't the desired behaviour, the normalization should only apply to Catch2's impl.

the current implementation has two problems:
  * `clang-cl` does not know `-ffile-prefix-map`, but in CMake it is
    reported as "Clang", so the compiler will warn about an unknown
    compiler option.
  * XCode's clang in CMake is reported as "AppleClang", so it is not picked
    up as "Clang", so it is not passed `-ffile-prefix-map`, even though
    it supports it.

Also changed the map so that the normalized `__FILE__` paths are the same
as what the approval tests normalize paths into.

Co-authored-by: Martin Hořeňovský <martin.horenovsky@gmail.com>

This is kinda messy, because there is no good way to signal to
the compiler that some code uses direct comparison of floating
point numbers intentionally, so instead we have to use diagnostic
pragmas.

We also have to over-suppress the test files, because Clang (and
possibly GCC) still issue warnings from template instantiation
even if the instantion site is under warning suppression, so the
template definition has to be under warning suppression as well.

Closes #2406