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/summary_test.go

@@ -26,6 +26,7 @@ func TestSummarize(t *testing.T) {
 		probeSSLInvalidHost    = netxlite.FailureSSLInvalidHostname
 		probeSSLInvalidCert    = netxlite.FailureSSLInvalidCertificate
 		probeSSLUnknownAuth    = netxlite.FailureSSLUnknownAuthority
+		probeAndroidEaiNoData  = netxlite.FailureAndroidDNSCacheNoData
 		tcpIP                  = "tcp_ip"
 		trueValue              = true
 	)
@@ -68,7 +69,7 @@ func TestSummarize(t *testing.T) {
 			Status:         webconnectivity.StatusAnomalyControlUnreachable,
 		},
 	}, {
-		name: "with non-existing website",
+		name: "with non-existing website (NXDOMAIN case)",
 		args: args{
 			tk: &webconnectivity.TestKeys{
 				DNSExperimentFailure: &probeNXDOMAIN,
@@ -84,6 +85,23 @@ func TestSummarize(t *testing.T) {
 			Status: webconnectivity.StatusSuccessNXDOMAIN |
 				webconnectivity.StatusExperimentDNS,
 		},
+	}, {
+		name: "with non-existing website (Android EAI_NODATA case)",
+		args: args{
+			tk: &webconnectivity.TestKeys{
+				DNSExperimentFailure: &probeAndroidEaiNoData,
+				DNSAnalysisResult: webconnectivity.DNSAnalysisResult{
+					DNSConsistency: &webconnectivity.DNSConsistent,
+				},
+			},
+		},
+		wantOut: webconnectivity.Summary{
+			BlockingReason: nil,
+			Blocking:       false,
+			Accessible:     &trueValue,
+			Status: webconnectivity.StatusSuccessNXDOMAIN |
+				webconnectivity.StatusExperimentDNS,
+		},
 	}, {
 		name: "with NXDOMAIN measured only by the probe",
 		args: args{