Extend gmock to turn off socket listener

On Linux, you'd generally expect this feature to work, but on Cray the
linker warns that the use of getaddrinfo() would require linking a
shared library at runtime. That never happens because we don't use the
socket listener feature, but we don't want people stressing over that
at build time.

Change-Id: I9c358a2923d7563809d471f2ea1767cf2e8bbe25