8367130: JDK builds broken by 8366837: Clean up gensrc by spp.Spp

Reviewed-by: liach

Author: erikj79

make/modules/java.base/gensrc/GensrcVarHandles.gmk

@@ -157,7 +157,7 @@ $(foreach t, $(PRIMITIVE_TYPES), \
 
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-GENSRC_VARHANDLEGUARDS := $(VARHANDLES_GENSRC_DIR)/VarHandleGuards.java
+GENSRC_VARHANDLEGUARDS := $(VARHANDLES_OUTPUT_DIR)/VarHandleGuards.java
 
 $(GENSRC_VARHANDLEGUARDS): $(BUILD_TOOLS_JDK)
 	$(call LogInfo, Generating $@)