Static-linked DR makes all SIGSEGV in exe fatal, thwarting app or client handlers

DR's signal handler has a check for SIGSEGV or SIGBUS:

        if (CLIENTS_EXIST() && is_in_client_lib(pc)) {

The problem is, that condition is always true for statically-linked DR. The code goes on to raise a fatal error with no chance of continuing, which breaks an app or client with a handler and expected SIGSEGV or SIGBUS.

I think we just have to disable that for static DR and live without a nice crash message as we have no real way to distinguish further.