Windows shm_open must be threadsafe

[elfenpiff]

Required information

Operating system:
Windows

Compiler version:
All

Observed result or behaviour:
When iox_shm_open/iox_shm_unlink is called concurrently in Windows it is possible that the underlying std::set openSharedMemorySegments is written concurrently in a non threadsafe way. This has to be protected by a mutex.

When Windows fails to create a shared memory segment the failure is observed when mapping it into the process and the error message just states the the file handle is invalid. So the user has no clue about the origin of the error.
This can happen when roudi creates the shm segments or when a named pipe for inter process communication between roudi and app is created.

Expected result or behaviour:
A threadsafe iox_shm_open and iox_shm_unlink function

A detailed error message which states why the shm segment creation failed.