Fix FOLLY_TLS under macosx and clang
Fix FOLLY_TLS under macosx and clang

Summary: Only include guard iphone simulator and iphone devices for folly_tls

Reviewed By: ldemailly

Differential Revision: D2872383

fb-gh-sync-id: 00fb8c1ee03a97037e92d20aeda75f2435d71f5a

Orvid/folly,Hincoin/folly,charsyam/folly,floxard/folly,floxard/folly,facebook/folly,Orvid/folly,brunomorishita/folly,facebook/folly,Hincoin/folly,Orvid/folly,brunomorishita/folly,Hincoin/folly,charsyam/folly,mqeizi/folly,floxard/folly,rklabs/folly,facebook/folly,Hincoin/folly,facebook/folly,rklabs/folly,brunomorishita/folly,charsyam/folly,charsyam/folly,mqeizi/folly,rklabs/folly,facebook/folly,brunomorishita/folly,rklabs/folly,Hincoin/folly,mqeizi/folly,rklabs/folly,Orvid/folly,brunomorishita/folly,mqeizi/folly,mqeizi/folly,Orvid/folly,floxard/folly,floxard/folly