IVGCVSW-3656 Build the reference backend by default

 * Changed the default value of the new ARMNNREF option to ON in
   the global makefile, so to always build the reference backend
   by default, thus keeping the same behaviour as of the previous
   releases

Change-Id: Id4941522ac7987c797ac8331ea421edb2a54287f
Signed-off-by: Matteo Martincigh <matteo.martincigh@arm.com>
diff --git a/cmake/GlobalConfig.cmake b/cmake/GlobalConfig.cmake
index c94d500..9c59abf 100644
--- a/cmake/GlobalConfig.cmake
+++ b/cmake/GlobalConfig.cmake
@@ -6,7 +6,7 @@
 option(BUILD_FOR_COVERAGE "Use no optimization and output .gcno and .gcda files" OFF)
 option(ARMCOMPUTENEON "Build with ARM Compute NEON support" OFF)
 option(ARMCOMPUTECL "Build with ARM Compute OpenCL support" OFF)
-option(ARMNNREF "Build with ArmNN reference support" OFF)
+option(ARMNNREF "Build with ArmNN reference support" ON)
 option(PROFILING_BACKEND_STREAMLINE "Forward the armNN profiling events to DS-5/Streamline as annotations" OFF)
 # options used for heap profiling and leak checking
 option(HEAP_PROFILING "Build with heap profiling enabled" OFF)