G will use llvm as its primary backend, and my intention follow the C ABI exactly so interop requires no work.
I haven't considered the standard library much beyond the fact that I would G to have its own that is inspired by the good parts of other languages. At first it would have to rely on C libraries.
G won't be able to support every way that the Go standard library works. But if you need everything Go has, then you probably want to use Go to begin with.