fix build on OS X
fix build on OS X

tjrileywisc/annoy,Houzz/annoy2,Houzz/annoy2,pombredanne/annoy,eddelbuettel/annoy,guitarmind/annoy,spotify/annoy,LongbinChen/annoy,LongbinChen/annoy2,Houzz/annoy2,guitarmind/annoy,pombredanne/annoy,LongbinChen/annoy,spotify/annoy,aimeida/annoy,codeaudit/annoy,BeifeiZhou/annoy,BeifeiZhou/annoy,LongbinChen/annoy,subu-cliqz/annoy,codeaudit/annoy,pombredanne/annoy,subu-cliqz/annoy,eddelbuettel/annoy,pombredanne/annoy,spotify/annoy,LongbinChen/annoy2,spotify/annoy,subu-cliqz/annoy,tjrileywisc/annoy,aimeida/annoy,subu-cliqz/annoy,eddelbuettel/annoy,tjrileywisc/annoy,aimeida/annoy,tjrileywisc/annoy,LongbinChen/annoy2,eddelbuettel/annoy,BeifeiZhou/annoy,codeaudit/annoy,guitarmind/annoy