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
