As discussing in [1], on template with "subpackages" as multilines will
report false positive on some packages will never be built.
There're multiple problems here:
- expanded "subpackages" will have an empty line if it has a newline
inside template
- "sed" expression couldn't work with multilines "subpackages"
Let's not quote "$subpkgs" and "$subpackages" in "printf" to let the
shell do expansion and trim the empty lines for us. And rewrite the
"sed" expression to work with multilines "subpackages"
[1]: https://github.com/void-linux/void-packages/pull/26939#issuecomment-739098547
