bpo-32627: Fix compile error when conflicting `_uuid` headers included (GH-11751)

(cherry picked from commit 6ffd9b05df)

Co-authored-by: ziheng <zihenglv@gmail.com>

Misc/NEWS.d/next/Library/2019-02-03-19-13-08.bpo-32627.b68f64.rst

@@ -0,0 +1 @@
+Fix compile error when ``_uuid`` headers conflicting included.

Modules/_uuidmodule.c

@@ -1,14 +1,17 @@
+/*
+ * Python UUID module that wraps libuuid -
+ * DCE compatible Universally Unique Identifier library.
+ */
+
 #define PY_SSIZE_T_CLEAN
 
 #include "Python.h"
 #ifdef HAVE_UUID_UUID_H
 #include <uuid/uuid.h>
-#endif
-#ifdef HAVE_UUID_H
+#elif defined(HAVE_UUID_H)
 #include <uuid.h>
 #endif
 
-
 static PyObject *
 py_uuid_generate_time_safe(PyObject *Py_UNUSED(context),
                            PyObject *Py_UNUSED(ignored))