`YKD_OPT=0` crashes with some yklua benchmarks

[ltratt]

e.g.:

YKD_OPT=0 YK_JITC=j2 harness.lua deltablue 10 12000

segfaults. The error is pinpointed in yklua's load_inst:

Starting deltablue benchmark ...

Thread 1 received signal SIGSEGV, Segmentation fault.
0x0000000000372d35 in load_inst ()
=> 0x0000000000372d35 <load_inst+5>:    8b 06                   mov    eax,DWORD PTR [rsi]
(rr) bt
#0  0x0000000000372d35 in load_inst ()
#1  0x000000000037331a in luaV_execute ()
...

Perhaps we're not handling outlining properly with the optimiser turned off or ...?