fixed build with g++ 5+ and ASAN enabled
fixed build with g++ 5+ and ASAN enabled

Summary:
Fixing by deleting unnecessary macro checks - folly already requires at least g++4.8
Closes https://github.com/facebook/folly/pull/338

Reviewed By: yfeldblum

Differential Revision: D2742024

Pulled By: fredemmott

fb-gh-sync-id: c0ecc7edceeebd1f972b0be4f4740214211f1c24

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