[bindings/go] add go.mod file

[chai2010]

Summary

go mod replace only works if target has go.mod:
https://github.com/golang/go/issues/30847

[aykevl]

This doesn't look like a correct Go module name:

$ go get llvm.org/llvm/bindings/go/llvm
go get: unrecognized import path "llvm.org/llvm/bindings/go/llvm": GOVCS disallows using svn for public llvm.org/llvm; see 'go help vcs'

I see two options:

1. Add the go-import meta tag, see https://gianarb.it/blog/go-mod-vanity-url for example.
2. Use github.com/llvm/llvm-project/llvm/bindings/go/llvm instead.

The first one might be the cleaner option, while the second one will likely be easier to implement.

[aykevl]

This is not relevant anymore since the Go bindings are removed. See D135436.

llvm/bindings/go/llvm/go.mod

+module llvm.org/llvm/bindings/go/llvm