Only require libc when building for unix

Author: dtolnay

Cargo.toml

@@ -20,9 +20,11 @@ filetime = "0.1"
 getopts = "0.2"
 log = "0.3"
 rustc-serialize = "0.3"
-libc = "0.2"
 tempdir = { version = "0.3", optional = true }
 
+[target."cfg(unix)".dependencies]
+libc = "0.2"
+
 [target."cfg(windows)".dependencies]
 miow = "0.2"
 winapi = "0.2"