Don't call DebugBreak when generating error codes

[derSeddy]

When an error code is generated with MPIR_Err_create_code_valist the Visual Studio debugger will stop. This behavior is quite annoying for us because we are trying to open a file with mpio and it is a legitimate scenario that this fails because we don't have the user rights to open the file.
We only use msmpi by linking against the release DLL thus we consider this behavor to be unexpected.

This is the line of code:

Microsoft-MPI/src/mpi/common/errutil.cpp

Line 343 in 7ff6bdc

DebugBreak();

We don't see a value in this behavior for end users, so we would just remove the line. But we think it would be fair to enclose it in #if DBG [...] #endif to at least only have the debugger stop when msmpi was build in debug mode.