Don't build tests in PDK build.

Change-Id: I8994be0938a3ce87a097669c28b232fd04b77a36
diff --git a/core/main.mk b/core/main.mk
index 3b5a023..dd5cfa3 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -993,9 +993,11 @@
 tests : host-tests target-tests
 
 # To catch more build breakage, check build tests modules in eng and userdebug builds.
+ifneq ($(TARGET_BUILD_PDK),true)
 ifneq ($(filter eng userdebug,$(TARGET_BUILD_VARIANT)),)
 droidcore : target-tests host-tests
 endif
+endif
 
 .PHONY: lintall