Suppress warnings from OpenCL include folder.

Fixes an odd compiler warning with half.hpp when included
from ComputeLibrary/include directory.

Signed-off-by: Matthew Bentham <matthew.bentham@arm.com>
Change-Id: I17d251bb68384c357ffb93ea8e63333564aba659
diff --git a/cmake/GlobalConfig.cmake b/cmake/GlobalConfig.cmake
index aa2ebc7..8e3b68d 100644
--- a/cmake/GlobalConfig.cmake
+++ b/cmake/GlobalConfig.cmake
@@ -279,7 +279,7 @@
     link_libraries(-L${ARMCOMPUTE_BUILD_DIR}/opencl-1.2-stubs)
     set(OPENCL_LIBRARIES OpenCL)
 
-    include_directories(${OPENCL_INCLUDE})
+    include_directories(SYSTEM ${OPENCL_INCLUDE})
 
     # Add preprocessor definition for ARM Compute OpenCL
     add_definitions(-DARMCOMPUTECL_ENABLED)