Add support for nios2

When compiling jack on nios2, compilation fails because NGREGS is not
defined. Since this is only for debug output on segmentation faults, stub
the debug print out like it's been done for other platforms before.

Inspired by
d11bb09529

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>

dbus/sigsegv.c

@@ -104,7 +104,7 @@ static void signal_segv(int signum, siginfo_t* info, void*ptr) {
     jack_error("info.si_errno = %d", info->si_errno);
     jack_error("info.si_code  = %d (%s)", info->si_code, si_code_str);
     jack_error("info.si_addr  = %p", info->si_addr);
-#if !defined(__alpha__) && !defined(__ia64__) && !defined(__FreeBSD_kernel__) && !defined(__arm__) && !defined(__hppa__) && !defined(__sh__) && !defined(__aarch64__)
+#if !defined(__alpha__) && !defined(__ia64__) && !defined(__FreeBSD_kernel__) && !defined(__arm__) && !defined(__hppa__) && !defined(__sh__) && !defined(__aarch64__) && !defined(nios2)
     for(i = 0; i < NGREG; i++)
         jack_error("reg[%02d]       = 0x" REGFORMAT, i, 
 #if defined(__powerpc64__)