cmake OpenCL detection and initialization

[ancahamuraru]

Medium-low priority issue

1. Test the Windows branches from gmxManageOpenCL.cmake for Linux
2. Have just one branch that would work for both Windows and Linux (and everything else)
3. Check OPENCL_DEFINITIONS for Windows - currently it throws errors when building the VS project
4. Check if both GMX_DETECT_OPENCL_AVAILABLE and OPENCL_FOUND are needed.
5. Decide if GMX_OPENCL_FORCE_LOCAL_HEADERS should be kept or not.

[dkarkoulis]

(1). Test the Windows branches from gmxManageOpenCL.cmake for Linux (2). Have just one branch that would work for both Windows and Linux (and everything else).

• Done for both. At least for Windows and Linux after your commit. I merged the Windows and Linux paths into one and cleaned up a bit.

(3). Check OPENCL_DEFINITIONS for Windows - currently it throws errors when building the VS project.

• Done. Not needed in Windows. It throws error because it is a gcc specific command. The issue is that in an OpenCL kernel there is a a comment inside another comment triggering endless warnings

(4). Check if both GMX_DETECT_OPENCL_AVAILABLE and OPENCL_FOUND are needed.

• Done. Fixed in the clean up. In fact now the detection works via find_package, so it returns OPENCL_FOUND. Nothing else is needed.

(5). Decide if GMX_OPENCL_FORCE_LOCAL_HEADERS should be kept or not.

• Needs to be discussed. The benefit is that someone can build the OpenCL part of Gromacs without downloading a whole SDK just for a handful of headers. I.e. a display driver that deploys libOpenCL is all that is needed.

[ancahamuraru]

(1) - (4) All done. (5). Decide if GMX_OPENCL_FORCE_LOCAL_HEADERS should be kept or not. GMX_OPENCL_FORCE_LOCAL_HEADERS should be removed. See comments below. Very low priority!!!

Needs to be discussed. The benefit is that someone can build the OpenCL part of Gromacs without downloading a whole SDK just for a handful of headers. I.e. a display driver that deploys libOpenCL is all that is needed.

This does not apply to Windows where you do need the SDK for the .lib files.

[ancahamuraru]

GMX_OPENCL_FORCE_LOCAL_HEADERS removed. See 434b55a4e58b594067fb52a9cdce50968c29674f.