Update CMake for Policy CMP0175

```
  Exactly one of PRE_BUILD, PRE_LINK, or POST_BUILD must be given.  Assuming
  POST_BUILD to preserve backward compatibility.
  Policy CMP0175 is not set: add_custom_command() rejects invalid arguments.
  Run "cmake --help-policy CMP0175" for policy details.  Use the cmake_policy
  command to set the policy and suppress this warning.
```