CMake: Don't look for OpenCL and CUDA packages if build isn't using them

Fixes: If -DBUILD_CUDA=OFF or -DBUILD_OPENCL=OFF is specified, irrelevant
warnings are output if these packages aren't available, even though they
won't be used.

libhmsbeagle/GPU/CMakeLists.txt

@@ -1,13 +1,17 @@
 
-find_package(OpenCL)
-if(OpenCL_FOUND AND BUILD_OPENCL)
-    message(STATUS "OpenCL Includes: ${OpenCL_INCLUDE_DIRS}")
-    message(STATUS "OpenCL Libraries: ${OpenCL_LIBRARIES}")
-    add_subdirectory("CMake_OpenCL")
-endif(OpenCL_FOUND AND BUILD_OPENCL)
+if(BUILD_OPENCL)
+	find_package(OpenCL)
+	if(OpenCL_FOUND)
+		message(STATUS "OpenCL Includes: ${OpenCL_INCLUDE_DIRS}")
+		message(STATUS "OpenCL Libraries: ${OpenCL_LIBRARIES}")
+		add_subdirectory("CMake_OpenCL")
+	endif(OpenCL_FOUND)
+endif(BUILD_OPENCL)
 
-find_package(CUDA)
-if(CUDA_FOUND AND BUILD_CUDA)
-    message(STATUS "CUDA Includes: ${CUDA_INCLUDE_DIRS}")
-    add_subdirectory("CMake_CUDA")
-endif(CUDA_FOUND AND BUILD_CUDA)
+if(BUILD_CUDA)
+	find_package(CUDA)
+	if(CUDA_FOUND)
+		message(STATUS "CUDA Includes: ${CUDA_INCLUDE_DIRS}")
+		add_subdirectory("CMake_CUDA")
+	endif(CUDA_FOUND)
+endif(BUILD_CUDA)