Darwin8 has no backtrace functionalities yet

--- src/sphinxutils.cpp
+++ src/sphinxutils.cpp
@@ -1364,6 +1364,9 @@
 	}
 	sphSafeInfo ( iFD, "Stack bottom = 0x%p, thread stack size = 0x%x", pMyStack, iStackSize );
 
+#ifndef SIGRETURN_FRAME_OFFSET
+	sphLogFatal ( "Cannot get stack frame pointer on this architecture" );
+#else
 	while ( pMyStack && !bSafe )
 	{
 		sphSafeInfo ( iFD, "begin of manual backtrace:" );
@@ -1421,6 +1424,7 @@
 
 		break;
 	}
+#endif
 
 #if HAVE_BACKTRACE
 	sphSafeInfo ( iFD, "begin of system backtrace:" );