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/netxlite/getaddrinfo_windows.go

@@ -0,0 +1,28 @@
+//go:build cgo && windows
+
+package netxlite
+
+//#include <ws2tcpip.h>
+import "C"
+
+import "syscall"
+
+const getaddrinfoAIFlags = C.AI_CANONNAME
+
+// Making constants available to Go code so we can run tests (it seems
+// it's not possible to import C directly in tests, sadly).
+const (
+	aiCanonname = C.AI_CANONNAME
+)
+
+// toError is the function that converts the return value from
+// the getaddrinfo function into a proper Go error.
+func (state *getaddrinfoState) toError(code int64, err error, goos string) error {
+	if err == nil {
+		// Implementation note: on Windows getaddrinfo directly
+		// returns what is basically a winsock2 error. So if there
+		// is no other error, just cast code to a syscall err.
+		err = syscall.Errno(code)
+	}
+	return newErrGetaddrinfo(int64(code), err)
+}