bpo-36648: fix mmap issue for VxWorks (GH-12394)

The mmap module set MAP_SHARED flag when map anonymous memory, however VxWorks
only support MAP_PRIVATE when map anonymous memory, this commit clear MAP_SHARED
and set MAP_PRIVATE.

Misc/NEWS.d/next/Library/2019-03-18-14-25-36.bpo-31904.ds3d67.rst

+Fix mmap fail for VxWorks

Modules/mmapmodule.c

@@ -1164,6 +1164,13 @@ new_mmap_object(PyTypeObject *type, PyObject *args, PyObject *kwdict)
 #ifdef MAP_ANONYMOUS
         /* BSD way to map anonymous memory */
         flags |= MAP_ANONYMOUS;
+
+        /* VxWorks only supports MAP_ANONYMOUS with MAP_PRIVATE flag */
+#ifdef __VXWORKS__
+        flags &= ~MAP_SHARED;
+        flags |= MAP_PRIVATE;
+#endif
+
 #else
         /* SVR4 method to map anonymous memory is to open /dev/zero */
         fd = devzero = _Py_open("/dev/zero", O_RDWR);