Allow to run checkbuild in sdk build.

Bug: 9594464
Change-Id: Ia02e7d8fc157cdfe2e065ce9e42a3800457f89f6
diff --git a/core/main.mk b/core/main.mk
index d5942ea..25ec74e 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -359,7 +359,7 @@
 sdk_repo_goal := $(strip $(filter sdk_repo,$(MAKECMDGOALS)))
 MAKECMDGOALS := $(strip $(filter-out sdk_repo,$(MAKECMDGOALS)))
 
-ifneq ($(words $(filter-out $(INTERNAL_MODIFIER_TARGETS),$(MAKECMDGOALS))),1)
+ifneq ($(words $(filter-out $(INTERNAL_MODIFIER_TARGETS) checkbuild,$(MAKECMDGOALS))),1)
 $(error The 'sdk' target may not be specified with any other targets)
 endif