osthread: suspend() and resume() code deduplication

[denizzzka]

Got rid of the repeating blocks:

        if ( t.m_addr != xxxx() && yyyyy( t.m_tmach ) != KERN_SUCCESS )
        {
            if ( !t.isRunning )
            {
                Thread.remove( t );
                return false;
            }
            onThreadError( "Unable to suspend thread" );
        }

System-related code moved to appropriate dedicated modules in last two commits: for review you can look except these comments - PR becomes clean and understandable

I removed these commits: a separate PR transfer will be done for moving

What is happening is part of the process of separating code from different platforms into different modules

[denizzzka]

At the moment it is difficult to do this: it clings to other symbols that have not yet been transferred to posix_impl

[denizzzka]

@QuantumSegfault This PR touches WASI implementation

[QuantumSegfault]

LGTM for WASI