Auto merge of rust-lang#34201 - sanxiyn:check-error-index, r=nagisa

Check error index in `make check`

This was checked in rustbuild but not in `make check`, causing passed-Travis-but-failed-Buildbot.

Author: bors

mk/tests.mk

@@ -276,6 +276,7 @@ check-stage$(1)-T-$(2)-H-$(3)-exec: \
 	check-stage$(1)-T-$(2)-H-$(3)-incremental-exec \
 	check-stage$(1)-T-$(2)-H-$(3)-ui-exec \
 	check-stage$(1)-T-$(2)-H-$(3)-doc-exec \
+	check-stage$(1)-T-$(2)-H-$(3)-doc-error-index-exec \
 	check-stage$(1)-T-$(2)-H-$(3)-pretty-exec
 
 ifndef CFG_DISABLE_CODEGEN_TESTS