[libc][stubs] Correct the stub definition of freeaddrinfo

When the real definition of freeaddrinfo (and other associated
functions) was moved to fdio, the libc source file definining
freeaddrinfo was left in the tree, even though there was no build rule
for it.

Additionally, the stub_freeaddrinfo function was not marked static.

This CL fixes both of these glitches.

Change-Id: If7a4f10f9faa6c3223a8a9c7c5fc6a9d9cfb12de

[zircon][musl] Remove getaddinfo() from libc and add a stub

Previously libc defined getaddrinfo() was defined in libc, but it wasn't
working properly. Removed it from libc, since it's defined and
implemented in libfdio.

Change-Id: Ib2aa8f71b6233266742fae68630e733b03559a57

[mxio][musl] Stub out socket calls

Change-Id: I171d6de67ec21d4462229bf6894ff456c2872471