Fix incremental make on OSX when lib files change
Fix incremental make on OSX when lib files change

Summary: @​danvk noticed that when you changed the lib files and than ran `make` (without a `make clean`) that the resulting binary would still use the old libraries. I looked into it and found an issue with incremental make on OSX.

Long story short, we want ocamlbuild to re-link the binary when the lib files change, since on OSX we rely on ocamlbuild to embed the lib files in the binary (`objcopy` is not available). However ocamlbuild doesn't understand that it needs to relink when non-ocaml dependencies change.
Closes https://github.com/facebook/flow/pull/840

Reviewed By: @​svcscm

Differential Revision: D2464340

Pulled By: @gabelevi

cesarandreu/flow,Fresheyeball/flow,mcanthony/flow-type,jamesgpearce/flow,jamesgpearce/flow,jamesgpearce/flow,mroch/flow,jamesgpearce/flow,asivitz/flow,gabelevi/flow,gabro/flow,jgrund/flow,darioajr/flow,mroch/flow,ylu1317/flow,gabro/flow,popham/flow,mroch/flow,shiftcars/flow,jgrund/flow,d14b3l/flow,claudiopro/flow,jeffmo/flow,facebook/flow,gabelevi/flow,chenglou/flow,samwgoldman/flow,OCamlPro/flow,facebook/flow,chenglou/flow,ylu1317/flow,jeffmo/flow,JonathanUsername/flow,gabelevi/flow,ForbesLindesay/flow,AgentME/flow,mcanthony/flow-type,ForbesLindesay/flow,TiddoLangerak/flow,jdelStrother/flow,jamesgpearce/flow,gabro/flow,samwgoldman/flow,jdelStrother/flow,ylu1317/flow,nmote/flow,gabelevi/flow,samwgoldman/flow,Fresheyeball/flow,JohnyDays/flow,AprilArcus/flow,popham/flow,fletcherw/flow,AprilArcus/flow,gabro/flow,shiftcars/flow,jgrund/flow,Fresheyeball/flow,graue/flow,claudiopro/flow,JonathanUsername/flow,jdelStrother/flow,popham/flow,popham/flow,cesarandreu/flow,JonathanUsername/flow,MichaelDeBoey/flow,jeffutter/flow,shiftcars/flow,facebook/flow,mroch/flow,samwgoldman/flow,fletcherw/flow,Eyyub/flow,chenglou/flow,cesarandreu/flow,fletcherw/flow,AprilArcus/flow,fletcherw/flow,Fresheyeball/flow,MichaelDeBoey/flow,facebook/flow,mroch/flow,jeffmo/flow,jeffutter/flow,claudiopro/flow,nmote/flow,graue/flow,ylu1317/flow,gabelevi/flow,chenglou/flow,fletcherw/flow,jeffmo/flow,nmote/flow,JohnyDays/flow,JohnyDays/flow,TiddoLangerak/flow,jgrund/flow,nmote/flow,jeffmo/flow,jeffutter/flow,samwgoldman/flow,chenglou/flow,shiftcars/flow,popham/flow,jamesgpearce/flow,jeffmo/flow,TiddoLangerak/flow,asivitz/flow,nmote/flow,AgentME/flow,asivitz/flow,ForbesLindesay/flow,cesarandreu/flow,jeffutter/flow,ForbesLindesay/flow,facebook/flow,Eyyub/flow,jgrund/flow,jamesgpearce/flow,nmote/flow,AprilArcus/flow,AprilArcus/flow,JohnyDays/flow,JonathanUsername/flow,mroch/flow,Eyyub/flow,samwgoldman/flow,MichaelDeBoey/flow,ForbesLindesay/flow,claudiopro/flow,fletcherw/flow,gabro/flow,jdelStrother/flow,nmote/flow,OCamlPro/flow,JonathanUsername/flow,shiftcars/flow,d14b3l/flow,d14b3l/flow,AgentME/flow,MichaelDeBoey/flow,AprilArcus/flow,JonathanUsername/flow,jdelStrother/flow,jgrund/flow,ForbesLindesay/flow,graue/flow,popham/flow,darioajr/flow,asivitz/flow,gabelevi/flow,facebook/flow,gabro/flow,MichaelDeBoey/flow,graue/flow,darioajr/flow,TiddoLangerak/flow,gabelevi/flow,samwgoldman/flow,shiftcars/flow,OCamlPro/flow,jdelStrother/flow,AgentME/flow,claudiopro/flow,mcanthony/flow-type,d14b3l/flow,d14b3l/flow,TiddoLangerak/flow,AgentME/flow,JonathanUsername/flow,graue/flow,darioajr/flow,popham/flow,OCamlPro/flow,mroch/flow,ylu1317/flow,d14b3l/flow,Eyyub/flow,mcanthony/flow-type,facebook/flow,graue/flow,chenglou/flow