Fix reentrancy bug in APC, ... introduces regression

### HHVM Version

swalk@labb-7:~/extra/play.040419a/hhvm$ hphp/hhvm/hhvm --version
HipHop VM 4.1.0-dev (rel)
Compiler: heads/master-0-g8ef41e8513de62b3a3d9c6628baa4ee0ca6df7ba
Repo schema: 11e451b6db41c73a6235725f3a828bf2225e1a7a

### Operating System and Version

Two hosts - x86 and aarch64. Both running Ubuntu 16.04
swalk@lab-7:~/extra/play.040419a/hhvm$ uname -a
Linux labb-7 4.4.0-138-generic #164-Ubuntu SMP Tue Oct 2 17:15:48 UTC 2018 aarch64 aarch64 aarch64 GNU/Linux

swalk@dellx3:~/play.040419a/hhvm$ uname -a
Linux dellx3 4.4.0-57-generic #78-Ubuntu SMP Fri Dec 9 23:50:32 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
### Standalone code, or other way to reproduce the problem

hphp/test/run -v -m interp
hphp/test/run -v -m interp -r
hphp/test/run -v -m jit -a '-vEval.JitPGO=0'
hphp/test/run -v -m jit -r -a '-vEval.JitPGO=0'
hphp/test/run -v -m jit -a '-vEval.JitPGO=1'
hphp/test/run -v -m jit -r -a '-vEval.JitPGO=1'

### Actual result

Post-processed report below. Columns line up with option sets above.

hphp/test/slow/apc-locking.php | F | F | F | F | F | F |

### Expected result

pass

Most likely introduced here
https://github.com/facebook/hhvm/commit/3d65e24106ea1c250103cf458b189c8f85a1dc98

swalk@lab-7:~/extra/play.040419a/hhvm$ ./hphp/hhvm/hhvm -c /mnt/diskb/swalk/play.040419a/hhvm/hphp/test/slow/config.ini -vEval.EnableArgsInBacktraces=true -vEval.EnableIntrinsicsExtension=true -vEval.HHIRInliningIgnoreHints=false -vRepo.Local.Mode=-- -vRepo.Central.Path=/mnt/diskb/swalk/play.040419a/hhvm/hphp/hhvm/verify.hhbc -vEval.Jit=true -vEval.ProfileHWEnable=false -vEval.HackCompilerExtractPath='/mnt/diskb/swalk/play.040419a/hhvm/hphp/hhvm/hackc_%{schema}' -vEval.EmbeddedDataExtractPath='/mnt/diskb/swalk/play.040419a/hhvm/hphp/hhvm/hhvm_%{type}_%{buildid}' -vResourceLimit.CoreFileSize=0 --file 'hphp/test/slow/apc-locking.php'
In main

Fatal error: Call to undefined function fb_call_user_func_async() in /mnt/diskb/swalk/play.040419a/hhvm/hphp/test/slow/apc-locking.php on line 41