make docs build depend on stdlibs-cache

Author: vchuravy

Makefile

@@ -116,7 +116,7 @@ stdlibs-cache-release stdlibs-cache-debug : stdlibs-cache-% : julia-%
 
 debug release : % : julia-% stdlibs-cache-%
 
-docs: julia-sysimg-$(JULIA_BUILD_MODE)
+docs: julia-sysimg-$(JULIA_BUILD_MODE) stdlibs-cache-$(JULIA_BUILD_MODE)
 	@$(MAKE) $(QUIET_MAKE) -C $(BUILDROOT)/doc JULIA_EXECUTABLE='$(call spawn,$(JULIA_EXECUTABLE_$(JULIA_BUILD_MODE))) --startup-file=no'
 
 docs-revise: