[hack] s/Unix.select/Sys_utils.select_non_intr/ in watchman.ml
[hack] s/Unix.select/Sys_utils.select_non_intr/ in watchman.ml

Summary:
We often use signals in Flow (and even Hack), so we should use
the wrapper which handles EINTR correctly

Reviewed By: alexchow

Differential Revision: D8211621

fbshipit-source-id: a8639e8435f46126450f6a01aa293c30373d27e3

AgentME/flow,mroch/flow,mroch/flow,facebook/flow,samwgoldman/flow,claudiopro/flow,nmote/flow,nmote/flow,gabelevi/flow,popham/flow,nmote/flow,gabelevi/flow,claudiopro/flow,gabelevi/flow,popham/flow,nmote/flow,jamesgpearce/flow,jamesgpearce/flow,JonathanUsername/flow,jamesgpearce/flow,JonathanUsername/flow,nmote/flow,facebook/flow,popham/flow,claudiopro/flow,popham/flow,gabelevi/flow,JonathanUsername/flow,claudiopro/flow,popham/flow,jamesgpearce/flow,JonathanUsername/flow,AgentME/flow,facebook/flow,facebook/flow,mroch/flow,AgentME/flow,samwgoldman/flow,facebook/flow,mroch/flow,samwgoldman/flow,facebook/flow,jamesgpearce/flow,claudiopro/flow,mroch/flow,JonathanUsername/flow,JonathanUsername/flow,gabelevi/flow,popham/flow,samwgoldman/flow,gabelevi/flow,samwgoldman/flow,gabelevi/flow,jamesgpearce/flow,AgentME/flow,mroch/flow,popham/flow,samwgoldman/flow,nmote/flow,nmote/flow,AgentME/flow,facebook/flow,jamesgpearce/flow,JonathanUsername/flow,mroch/flow,samwgoldman/flow