Enable OpenCL for Mac, by default; keep disabled for BSD

CMAKE_HOST_SYSTEM_NAME (uname -s) on macOS returns Darwin, even though
it is a BSD variant.

Author: dakcarto

CMakeLists.txt

@@ -30,11 +30,11 @@ MESSAGE(STATUS "QGIS version: ${COMPLETE_VERSION} ${RELEASE_NAME} (${QGIS_VERSIO
 #############################################################
 # Configure OpenCL if available
 SET(HAVE_OPENCL FALSE)
-IF (APPLE OR ${CMAKE_HOST_SYSTEM_NAME} MATCHES "BSD$")
+IF (${CMAKE_HOST_SYSTEM_NAME} MATCHES "BSD$")
   OPTION(USE_OPENCL "Use OpenCL" OFF)
-ELSE (APPLE OR ${CMAKE_HOST_SYSTEM_NAME} MATCHES "BSD$")
+ELSE (${CMAKE_HOST_SYSTEM_NAME} MATCHES "BSD$")
   OPTION(USE_OPENCL "Use OpenCL" ON)
-ENDIF (APPLE OR ${CMAKE_HOST_SYSTEM_NAME} MATCHES "BSD$")
+ENDIF (${CMAKE_HOST_SYSTEM_NAME} MATCHES "BSD$")
 IF (USE_OPENCL)
     FIND_PACKAGE(OpenCL)
     IF(${OpenCL_FOUND})