This is the implementation for the specification change done in a recent
commit.

May occur when not mapping a Void variable in the control system so it
is being optimised out.

This happens if the control system adapter optimises out the PV.

A PV which is received by a module and also used as a trigger for a
DeviceModule was "deleted" from the model, if the module is unregistered
from its owner. This deletion is now prevented by adding a trigger
relationship to the model (which was anyway missing).

Note: the "deletion" never was a real deletion, instead only all
relationships are removed. As a consequence, the DeviceModule was still
pointing to the "deleted" vertex resulting in a wrong connection later.

* Use correct of version pthread_setname_np depending on platform.

On Linux, this function takes two parameters. On most other platforms
(including all BSD-based platforms) it only takes a single parameter.

* Omit -Wl,--export-dynamic flag on macOS.

This flag is not supported on Clang / LLVM and on macOS it is not needed
anway because exporting all symbols is the default behavior.

When using Clang on other platforms (e.g. Linux) --export_dynamic or
-rdynamic might have to be specified instead.

* clang compiler compatibility

Co-authored-by: Sebastian Marsching <sebastian.marsching-git-2016@aquenos.com>