graphics/darktable: Update to 5.0.0

Release notes:
* https://github.com/darktable-org/darktable/releases/tag/release-5.0.0
* https://github.com/darktable-org/darktable/releases/tag/release-5.0.1

At the same time, the port stops to require GCC to compile and use
LLVM/Clang.