Colorimetry constants can be initialized after IccProfile::s_connectionSpace
when LTO is enabled. It's okay with the C++ standard.

As a way around it, this change moves the CIEXYZD50 constant to the
IccProfile where it's actually needed.

We need to reconsider how the constants are defined, e.g. have static
getters or use constexpr. But as a short term solution, this should be
fine.

BUG: 499789

Co-authored-by: Xaver Hugl <xaver.hugl@gmail.com>