Improved chain.sh to remove old .gb files first

Made the first step of the chain.sh remove the generated .gb file from
previous runs. This ensures that if the goto-cc step fails, misleading
results are not generated.

Author: thk123

regression/goto-instrument-typedef/chain.sh

@@ -8,6 +8,7 @@ GI=$SRC/goto-instrument/goto-instrument
 OPTS=$1
 NAME=${2%.c}
 
+rm $NAME.gb
 $GC $NAME.c --function fun -o $NAME.gb
 echo $GI $OPTS $NAME.gb
 $GI $OPTS $NAME.gb