netxlite: call getaddrinfo and handle platform-specific oddities (#764)

This commit changes our system resolver to call getaddrinfo directly when CGO is enabled. This change allows us to:

1. obtain the CNAME easily

2. obtain the real getaddrinfo retval

3. handle platform specific oddities such as `EAI_NODATA`
returned on Android devices

See https://github.com/ooni/probe/issues/2029 and https://github.com/ooni/probe/issues/2029#issuecomment-1140258729 in particular.

See https://github.com/ooni/probe/issues/2033 for documentation regarding the desire to see `getaddrinfo`'s retval.

See https://github.com/ooni/probe/issues/2118 for possible follow-up changes.

.github/workflows/netxlite.yml

@@ -1,6 +1,9 @@
-# netxlite runs unit and integration tests on our fundamental net library
+# Runs unit and integration tests for our fundamental networking library.
 name: netxlite
 on:
+  # Because we link libc explicitly for getaddrinfo, we SHOULD run
+  # these checks for every PR to ensure we still compile.
+  pull_request:
   push:
     branches:
       - "master"