ROCMOPS-924 centos-6.10 support for opencl_on_rocclr build

Fix a build error in centos 6.10. When linking, ld cannot find function
clock_getres. This function is from librt (for glibc version before 2.17).

Change-Id: I698f768d0618a054d5d0fc73b9f1916a7ce542fb

rocclr/CMakeLists.txt

@@ -198,6 +198,11 @@ endif()
 
 if (UNIX)
     set(ROCclr_DEFAULT_INSTALL_PREFIX "/opt/rocm/rocclr")
+
+    find_library(LIBRT rt)
+    if (LIBRT)
+        target_link_libraries(amdrocclr_static PUBLIC ${LIBRT})
+    endif()
 endif()
 #comment out as it's not available in cmake 3.5
 #if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)