mk: Account for libdir change on windows
mk: Account for libdir change on windows

The recent change of libdir on windows was accidentally not propagated to
`make dist` and related commands. This commit touches that up!

Closes #29640

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