mk: Fix doc tests for multiple targets

It only really makes sense to run tests for the build target anyway because it's
not guaranteed that you can execute other targets.

This is blocking the next snapshot

Author: alexcrichton

mk/tests.mk

@@ -745,21 +745,27 @@ CRATE_DOC_LIB-extra = $(EXTRALIB_CRATE)
 
 define DEF_CRATE_DOC_TEST
 
-check-stage$(1)-T-$(2)-H-$(2)-doc-$(3)-exec: $$(call TEST_OK_FILE,$(1),$(2),$(2),doc-$(3))
+check-stage$(1)-T-$(2)-H-$(3)-doc-$(4)-exec: $$(call TEST_OK_FILE,$(1),$(2),$(3),doc-$(4))
 
-$$(call TEST_OK_FILE,$(1),$(2),$(2),doc-$(3)):		\
-	        $$(TEST_SREQ$(1)_T_$(2)_H_$(2))		\
-		$$(HBIN$(1)_H_$(2))/rustdoc$$(X_$(2))
-	@$$(call E, run doc-$(3) [$(2)])
-	$$(Q)$$(HBIN$(1)_H_$(2))/rustdoc$$(X_$(2)) --test \
-	    $$(CRATE_DOC_LIB-$(3)) && touch $$@
+ifeq ($(2),$$(CFG_BUILD))
+$$(call TEST_OK_FILE,$(1),$(2),$(3),doc-$(4)):		\
+	        $$(TEST_SREQ$(1)_T_$(2)_H_$(3))		\
+		$$(HBIN$(1)_H_$(3))/rustdoc$$(X_$(3))
+	@$$(call E, run doc-$(4) [$(2)])
+	$$(Q)$$(HBIN$(1)_H_$(3))/rustdoc$$(X_$(3)) --test \
+	    $$(CRATE_DOC_LIB-$(4)) && touch $$@
+else
+$$(call TEST_OK_FILE,$(1),$(2),$(3),doc-$(4)):
+	touch $$@
+endif
 
 endef
 
 $(foreach host,$(CFG_HOST), \
- $(foreach stage,$(STAGES), \
-  $(foreach crate,$(TEST_DOC_CRATES), \
-   $(eval $(call DEF_CRATE_DOC_TEST,$(stage),$(host),$(crate))))))
+ $(foreach target,$(CFG_TARGET), \
+  $(foreach stage,$(STAGES), \
+   $(foreach crate,$(TEST_DOC_CRATES), \
+    $(eval $(call DEF_CRATE_DOC_TEST,$(stage),$(target),$(host),$(crate)))))))
 
 ######################################################################
 # Extracting tests for docs