Flags in package-manager-build-settings

I was really impressed with swift-evolution/0238-package-manager-build-settings.md at master · apple/swift-evolution · GitHub however, it doesn't look like I can add the following flags into my library: -Xswiftc -I/usr/local/include/<somelib>/ and -Xlinker -L/usr/local/lib without going through unsafe flags which disallows my library to be used as a dependency.

Can these flags be added? Or is there a way to express them in a modulemap?