llvm is not [always] used in concurrent recompilation

[vivanishin]

cd llv8-regtests/inlining/the-simplest
d8 --llvm-filter=foo* inl.js  # llv8 does not kick in
d8 --llvm-filter=foo* inl.js --noconcurrent-recompilation --noconcurrent-osr # now it does