Fix the detection of preadv and pwritev on OSX in OSS
authorChristopher Dykes <cdykes@fb.com>
Fri, 20 May 2016 21:26:38 +0000 (14:26 -0700)
committerFacebook Github Bot 3 <facebook-github-bot-3-bot@fb.com>
Fri, 20 May 2016 21:38:32 +0000 (14:38 -0700)
commitf464accb69e96176e5a313da5d24d76ee5297ca2
tree8e72860b9531cb58da5b0ccc92aaf5b242cb5ceb
parent10c767929b2c3d7340f7f0db15da7f983a08fe51
Fix the detection of preadv and pwritev on OSX in OSS

Summary:
The configure script doesn't define `FOLLY_HAVE_PREADV` if `preadv` isn't supported, so these checks were wrong. Undefined defines expand to `0`, so this is safe.
Fixes https://github.com/facebook/folly/issues/412

Reviewed By: mzlee, yfeldblum

Differential Revision: D3329405

fbshipit-source-id: faee8951c68d4c67e06e7720dfc142e63a9dbd9f
folly/portability/SysUio.cpp
folly/portability/SysUio.h