CLocatorAPI::setup_fs_path symlinking ignores CMAKE_INSTALL_DATAROOTDIR

Created by: OPNA2608

Describe the bug Introduced by https://github.com/OpenXRay/xray-16/pull/739, https://github.com/OpenXRay/xray-16/commit/c076c7a5780acdf1c95e5cb51982ff1ba7bb0d82: https://github.com/OpenXRay/xray-16/blob/c393d2d8530f8f6795852affc56b33d9a3d6dd61/src/xrCore/LocatorAPI.cpp#L873-L887

This assumes that fsgame.ltx and gamedata/shaders/gl are always installed to /usr/share/openxray, which is not the case: https://github.com/OpenXRay/xray-16/blob/83c0397f2b51e12f1507697c1f2a8e1095a62f5a/res/CMakeLists.txt#L3-L5

Building with a different CMAKE_INSTALL_PREFIX or CMAKE_INSTALL_DATAROOTDIR breaks this assumption and produces bogus symlinks.

To Reproduce Steps to reproduce the behavior:

Build with cmake -DCMAKE_INSTALL_PREFIX=/usr/local and install
Run xr_3da in an environment where the pref path in the user's home doesn't exist
Observe that it produces bogus symlinks to /usr/share/openxray, while the files were actually installed to /usr/local/share/openxray

Expected behavior The CMake script should make the value of CMAKE_INSTALL_FULL_DATAROOTDIR available to this code via a define (either under this or a less CMake-specific name) and the symlinking calls should be

symlink(CMAKE_INSTALL_FULL_DATAROOTDIR "/openxray/...", tmp);

Screenshots

BugTrap error report n/a

Desktop (please complete the following information):

OS: NixOS unstable
OpenXRay build version 83c0397f

Additional context Should be replicable on any Linux system.