Auto merge of rust-lang#768 - tamird:bring-back-target-vendor, r=alexcrichton

Bring back cfg_target_vendor, which is still used

r? @alexcrichton rust-lang#44515 (comment)

Author: bors

src/lib.rs

@@ -83,7 +83,7 @@
 ))]
 
 // Attributes needed when building as part of the standard library
-#![cfg_attr(feature = "stdbuild", feature(no_std, staged_api, custom_attribute))]
+#![cfg_attr(feature = "stdbuild", feature(no_std, staged_api, custom_attribute, cfg_target_vendor))]
 #![cfg_attr(feature = "stdbuild", feature(link_cfg))]
 #![cfg_attr(feature = "stdbuild", no_std)]
 #![cfg_attr(feature = "stdbuild", staged_api)]