COMPMID-417 - Fix for the config_id default string

The empty string used by default for config_id caused a memory corruption on Android.

Change-Id: Ib9c764c8a8f7009936071f8c8fec1653bb000f90
Reviewed-on: http://mpd-gerrit.cambridge.arm.com/89262
Tested-by: Kaizen <jeremy.johnson+kaizengerrit@arm.com>
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Reviewed-by: Anthony Barbier <anthony.barbier@arm.com>
diff --git a/arm_compute/core/CL/CLTypes.h b/arm_compute/core/CL/CLTypes.h
index cf11f6e..05f9e2e 100644
--- a/arm_compute/core/CL/CLTypes.h
+++ b/arm_compute/core/CL/CLTypes.h
@@ -24,8 +24,13 @@
 #ifndef __ARM_COMPUTE_CL_TYPES_H__
 #define __ARM_COMPUTE_CL_TYPES_H__
 
+#include <string>
+
 namespace arm_compute
 {
+/** Default string for the CLKernel configuration id */
+static const std::string default_config_id = "no_config_id";
+
 /** Available GPU Targets */
 enum class GPUTarget
 {