Use the new Unicode API

* Replace PyUnicode_FromUnicode(NULL, 0) by PyUnicode_New(0, 0)
 * Replce PyUnicode_FromUnicode(str, len) by PyUnicode_FromWideChar(str, len)
 * Replace Py_UNICODE by wchar_t
 * posix_putenv() uses PyUnicode_FromFormat() to create the string, instead
   of PyUnicode_FromUnicode() + _snwprintf()

Modules/socketmodule.c

@@ -3900,7 +3900,7 @@ socket_gethostname(PyObject *self, PyObject *unused)
     PyObject *result;
 
     if (GetComputerNameExW(ComputerNamePhysicalDnsHostname, buf, &size))
-        return PyUnicode_FromUnicode(buf, size);
+        return PyUnicode_FromWideChar(buf, size);
 
     if (GetLastError() != ERROR_MORE_DATA)
         return PyErr_SetFromWindowsErr(0);