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.

internal/engine/experiment/webconnectivity/dnsanalysis_test.go

@@ -14,6 +14,7 @@ func TestDNSAnalysis(t *testing.T) {
 	measurementFailure := netxlite.FailureDNSNXDOMAINError
 	controlFailure := webconnectivity.DNSNameError
 	eofFailure := io.EOF.Error()
+	androidEaiNoData := netxlite.FailureAndroidDNSCacheNoData
 	type args struct {
 		URL         *url.URL
 		measurement webconnectivity.DNSLookupResult
@@ -57,7 +58,7 @@ func TestDNSAnalysis(t *testing.T) {
 			DNSConsistency: &webconnectivity.DNSInconsistent,
 		},
 	}, {
-		name: "when the failures are compatible",
+		name: "when the failures are compatible (NXDOMAIN case)",
 		args: args{
 			URL: &url.URL{
 				Host: "www.kerneltrap.org",
@@ -74,6 +75,24 @@ func TestDNSAnalysis(t *testing.T) {
 		wantOut: webconnectivity.DNSAnalysisResult{
 			DNSConsistency: &webconnectivity.DNSConsistent,
 		},
+	}, {
+		name: "when the failures are compatible (Android EAI_NODATA case)",
+		args: args{
+			URL: &url.URL{
+				Host: "www.kerneltrap.org",
+			},
+			measurement: webconnectivity.DNSLookupResult{
+				Failure: &androidEaiNoData,
+			},
+			control: webconnectivity.ControlResponse{
+				DNS: webconnectivity.ControlDNSResult{
+					Failure: &controlFailure,
+				},
+			},
+		},
+		wantOut: webconnectivity.DNSAnalysisResult{
+			DNSConsistency: &webconnectivity.DNSConsistent,
+		},
 	}, {
 		name: "when the ASNs are equal",
 		args: args{