[QGIS-Developer] OpenCL and macOS

[Tom Elwertowski]

Hi all,

A recent change added OpenCL. Compilation fails on macOS because Apple 
provides v1.2 (macOS 10.13) while QGIS seems to require v2. Adding a 
version to FIND_PACKAGE will fix the macOS compile and not use OpenCL.

Apple has deprecated OpenCL in favor of its own Metal technology. OpenCL 
will remain for macOS 10.14 (Mojave, fall 2018) but may be removed after 
fall 2019.

For the future, either OpenCL must remain an optional QGIS feature in 
order to support macOS or the API needs to be abstracted so that macOS 
can use Metal while other OSs use OpenCL.

Tom
LinkedIn: https://www.linkedin.com/in/thomas-elwertowski-a0886032