mk: Prefer target libs coming from their host
mk: Prefer target libs coming from their host

It looks like the target libs aren't actually the same across hosts so instead
of always packaging the target libs from CFG_BUILD take the target libs from the
host if we have them and then only failing that do we take them from CFG_BUILD.

Closes #29228

graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust