Auto merge of #5448 - ehuss:debug_env, r=alexcrichton
authorbors <bors@rust-lang.org>
Tue, 1 May 2018 03:49:32 +0000 (03:49 +0000)
committerbors <bors@rust-lang.org>
Tue, 1 May 2018 03:49:32 +0000 (03:49 +0000)
Fix "DEBUG" env var in build.rs for debug=0

Fixes #5370


Trivial merge