Merge pull request #5755 from ahedberg/unix_sockets_optional

BUILD

Makefile

binding.gyp

build.yaml

config.m4

gRPC.podspec

grpc.gemspec

include/grpc/impl/codegen/port_platform.h

package.json

package.xml

src/core/client_config/resolvers/sockaddr_resolver.c

src/core/iomgr/endpoint_pair_posix.c

src/core/iomgr/resolve_address_posix.c

src/core/iomgr/sockaddr_utils.c

src/core/iomgr/tcp_client_posix.c

src/core/iomgr/tcp_server_posix.c

src/core/iomgr/udp_server.c

src/core/iomgr/unix_sockets_posix.c

src/core/iomgr/unix_sockets_posix.h

src/core/iomgr/unix_sockets_posix_noop.c