BUG#26701 check-cpu compile flags in x86-64 doesn't support gcc < 3.4,

apply suggestion from jocelyn fournier

BUILD/check-cpu

@@ -179,8 +179,15 @@ check_cpu () {
                     check_cpu_args='-mcpu=$cpu_arg -mtune=$cpu_arg'
             ;;
           x86_64-*)
+                case "$cc_verno" in
+                      3.4*|3.5*|4.*)
                             check_cpu_args='-mtune=$cpu_arg'
                             ;;
+                      *)
+                            check_cpu_args='-mcpu=$cpu_arg'
+                            ;;
+            esac
+            ;;
           *)
             check_cpu_cflags=""
             return