New review comment by Johnnynator on void-packages repository

https://github.com/void-linux/void-packages/pull/31687#discussion_r660022541

Comment:
Imo add the last few lines as
```bash
post_build() {
	rm -f swig/python/*_wrap.cpp
	make -C swig/python generate
	cd swig/python
	make ${makejobs} PYTHON=python3 ${makejobs}
}
```
and do not define `do_build` at all