Ensure building and running on non-IPv6 capable hosts works

* src/process.c (Fmake_network_process) [AF_INET6]: Only build ::1
localhost when IPv6 is supported.
(Fnetwork_lookup_address_info) [AF_INET6]: Move check for Qipv6 inside
ifdef, since its definition depends on AF_INET6.  Don't return IPv6
addresses when they're not supported.

* test/src/process-tests.el (lookup-family-specification,
lookup-google): Only do IPv6 lookup if IPv6 is supported.
1 job for master in 57 minutes and 38 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #4145
test-all

00:57:38

 
Name Stage Failure
failed
test-all Test
make[2]: *** [check-doit] Error 1
Makefile:319: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:294: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
make: *** [check-expensive] Error 2
Makefile:959: recipe for target 'check-expensive' failed
ERROR: Job failed: exit code 1