Fix hang on undefined symbol in rmb under pragma undefextern Problem in the pass4.c implementation led to an infinite loop if any instructions failed to resolve. Instead, if a pass through the loop fails to resolve anything, bail out since it's clearly pointless to continue trying.

\.exe$
\.o$
\.d$
\.a$
~$
\.orig$
/lwbasic$
/lwlink$
/lwobjdump$
/lwar$
/lwasm$
/lwcc/lwcc$
/lwcc/lwcpp$