mman: disable memfd_create declaration

libc/sysdeps/linux/common/bits/mman-shared.h

@@ -40,9 +40,11 @@
 
 __BEGIN_DECLS
 
+#if 0
 /* Create a new memory file descriptor.  NAME is a name for debugging.
    FLAGS is a combination of the MFD_* constants.  */
 int memfd_create (const char *__name, unsigned int __flags) __THROW;
+#endif
 
 /* Lock pages from ADDR (inclusive) to ADDR + LENGTH (exclusive) into
    memory.  FLAGS is a combination of the MLOCK_* flags above.  */