[PATCH 6] Fixes for headers included in C++

[chrisj at rtems.org]

Hi,

Looking at an EPICS utility exposed some issues with RTEMS 5 headers
when included in C++ programs. These patches address some of the issues
with RTEMS 6 headers when included in C++.

I tested this by generating a C++ source file of all the headers
for an installed Versal (aarch64) BSP. Some defines and a few
headers that needed to be include before others was added. The
headers that should not be directly included were removed.

I did not test SMP or MP. These should be checked and any
issues fixed.

The testing exposed some installed header issues that have also been
resolved.

The tickets 4705 and 4706 are for this work. It is not complete
and we should check it before releasing RTEMS 6. It is hard to sort
out in releases.

Chris