Check for sicons() availability properly.
Instead of hardcoding knowledge about glibc versions, check for the presence of sincos with CMake.
- use HAVE_SINCOS macro in files that call either sincos or sin and cos
- remove qDebug message about sincos, since it's a configure time choice and not relevant for users (and depending on compiler optimizations, also innacurate)
This means sincos will now be detected and properly used on more platforms, such as musl libc.