Auto merge of #1037 - alexcrichton:fix, r=alexcrichton

Fix a #[cfg] attribute

It looks like this was a mistake of #930 but should be easy to fix!

Author: bors

src/unix/mod.rs

@@ -310,7 +310,7 @@ cfg_if! {
         // Since we don't use -nodefaultlibs on Rumprun, libc is always pulled
         // in automatically by the linker. We avoid passing it explicitly, as it
         // causes some versions of binutils to crash with an assertion failure.
-        #[cfg_attr(feature = "stdbuild", target_vendor = "rumprun")]
+        #[cfg_attr(feature = "stdbuild", cfg(target_vendor = "rumprun"))]
         #[link(name = "m")]
         extern {}
     } else if #[cfg(any(target_os = "macos",