OK, direct the annoying traces to the output folder

Otherwise it was getting messy to distinguish between trace-events
and trace-<pid> in the .gitignore.

Now only the latest trace will be kept, with a fixed name.

run

@@ -25,7 +25,8 @@ initramfs=false
 memory=256M
 nographic=true
 root=''
-while getopts a:c:DdE:e:f:G:ghIiKkm:x OPT; do
+trace_enable=''
+while getopts a:c:DdE:e:f:G:ghIiKkm:T:x OPT; do
   case "$OPT" in
     a)
       arch="$OPTARG"
@@ -78,6 +79,9 @@ while getopts a:c:DdE:e:f:G:ghIiKkm:x OPT; do
     m)
       memory="$OPTARG"
       ;;
+    T)
+      trace_enable="$OPTARG"
+      ;;
     x)
       nographic=false
       ;;
@@ -169,6 +173,7 @@ ${debug_vm} \
 -monitor telnet::45454,server,nowait \
 -netdev user,hostfwd=tcp::45455-:45455,hostfwd=tcp::45456-:22,id=net0 \
 -smp ${cpus} \
+-trace enable=${trace_enable},file='${lkmc_out_dir}/trace.bin' \
 -virtfs local,path=9p,mount_tag=host_scratch,security_model=mapped,id=host_scratch \
 -virtfs local,path=${out_dir}/build,mount_tag=host_out,security_model=mapped,id=host_out \
 "