[NFC] Adding a new wrapper for getaddrinfo

Summary: This patch adds a new wrapper for getaddrinfo which returns a std::vector of SocketAddresses. While this patch doesn't add any uses of the new function, I have two separable patches that are dependent on this, so I put it in its own patch.

Reviewers: zturner

Reviewed By: zturner

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D31822

llvm-svn: 300112