8254144: Non-x86 Zero builds fail with return-type warning in os_linu…

…x_zero.cpp

Reviewed-by: zgu

src/hotspot/os_cpu/linux_zero/os_linux_zero.cpp

@@ -480,6 +480,7 @@ extern "C" {
     long long unsigned int oldval,
     long long unsigned int newval) {
     ShouldNotCallThis();
+    return 0; // silence compiler compiler warnings
   }
 };
 #endif // !_LP64