Merge r1561260 from trunk:

  *) Fix POSIX shared memory (shm_open) use for named shared memory.
     PR 55928. [Jozef Hatala <jh-asf skrt org>]

Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.5.x@1561261 13f79535-47bb-0310-9956-ffa450edef68