[GPU-Plugin] Add load balancing search to gpu_hist. Add compressed iterator. (#2504)

cmake/Utils.cmake

@@ -56,6 +56,7 @@ endfunction(set_default_configuration_release)
 
 function(format_gencode_flags flags out)
   foreach(ver ${flags})
-    set(${out} "${${out}}-gencode arch=compute_${ver},code=sm_${ver};" PARENT_SCOPE)
+    set(${out} "${${out}}-gencode arch=compute_${ver},code=sm_${ver};")
   endforeach()
+  set(${out} "${${out}}" PARENT_SCOPE)
 endfunction(format_gencode_flags flags)