Step towards working `arc diff --background 1` on Windows
Step towards working `arc diff --background 1` on Windows

Summary:
Running `a.php` from command line doesn't work on Windows, we need to run `php a.php`.
This shouldn't break other OSes.

Test Plan:
  $ arc diff --background 1

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3544

aik099/arcanist,zhihu/arcanist,haskell-infra/arcanist,PageUpPeopleOrg/arcanist-patches,zhihu/arcanist,Khan/arcanist,Khan/arcanist,fivestars/arcanist,dguo-coursera/arcanist,hach-que/arcanist,wxstars/arcanist,Symplicity/arcanist,dguo-coursera/arcanist,folsom-labs/arcanist,wikimedia/phabricator-arcanist,folsom-labs/arcanist,memsql/arcanist,phacility/arcanist,kevinseelbach/arcanist,wikimedia/phabricator-arcanist,hach-que/arcanist,Symplicity/arcanist,jra3/arcanist,codelabs-ch/arcanist,uber/arcanist,codelabs-ch/arcanist,uber/arcanist,zhihu/arcanist,eSpark/arcanist,wikimedia/phabricator-arcanist,dguo-coursera/arcanist,alexmv/arcanist,chundongwang/arcanist,r4nt/arcanist,aik099/arcanist,r4nt/arcanist,eSpark/arcanist,jra3/arcanist,chundongwang/arcanist,coursera/arcanist,KieranHayes/arcanist,wharris/arcanist,alexmv/arcanist,wxstars/arcanist,sneakpeeq/arcanist,julkiewicz/arcanist,hach-que/arcanist,jra3/arcanist,wharris/arcanist,haskell-infra/arcanist,wharris/arcanist,phacility/arcanist,chundongwang/arcanist,calblueprint/arcanist,folsom-labs/arcanist,KieranHayes/arcanist,Symplicity/arcanist,alexmv/arcanist,zhihu/arcanist,coursera/arcanist,haskell-infra/arcanist,wxstars/arcanist,wikimedia/phabricator-arcanist,Khan/arcanist,coursera/arcanist,chundongwang/arcanist,dguo-coursera/arcanist,KieranHayes/arcanist,phacility/arcanist,memsql/arcanist,julkiewicz/arcanist,r4nt/arcanist,fivestars/arcanist,wxstars/arcanist,jra3/arcanist,PageUpPeopleOrg/arcanist-patches,eSpark/arcanist,alexmv/arcanist,memsql/arcanist,Khan/arcanist,codelabs-ch/arcanist,sneakpeeq/arcanist,memsql/arcanist,r4nt/arcanist,aik099/arcanist,hach-que/arcanist,julkiewicz/arcanist,codelabs-ch/arcanist,coursera/arcanist,kevinseelbach/arcanist,sneakpeeq/arcanist,julkiewicz/arcanist,PageUpPeopleOrg/arcanist-patches,kevinseelbach/arcanist,calblueprint/arcanist,kevinseelbach/arcanist,uber/arcanist,codelabs-ch/arcanist,calblueprint/arcanist,fivestars/arcanist,calblueprint/arcanist,phacility/arcanist,uber/arcanist,Symplicity/arcanist,PageUpPeopleOrg/arcanist-patches,wharris/arcanist,KieranHayes/arcanist,folsom-labs/arcanist,eSpark/arcanist,haskell-infra/arcanist,fivestars/arcanist,sneakpeeq/arcanist,aik099/arcanist,phacility/arcanist