[LibOS,Pal] Improve recursive Make calls

Do not declare the result of the recursive Make call as "phony" to avoid
unnecessary rebuilds. Due to the missing dependency information we of
course still need to always recurse.

LibOS/shim/src/Makefile

@@ -88,10 +88,13 @@ libsysdb_debug.so: $(addsuffix .o,$(filter-out syscallas,$(objs))) \
 	@mkdir -p .lib
 	$(call cmd,ln_sf)
 
-.PHONY: $(graphene_lib)
-$(graphene_lib): .lib/host_endian.h
+.PHONY: graphene_lib_recurse
+graphene_lib_recurse: .lib/host_endian.h
 	$(MAKE) -C ../../../Pal/lib target=$(abspath .lib)/
 
+$(graphene_lib): graphene_lib_recurse
+	@true
+
 libsysdb.a: $(addsuffix .o,$(objs))
 	$(call cmd,ar_a_o)
 else

Pal/src/Makefile

@@ -83,14 +83,20 @@ $(LIB_DIR)/host_endian.h: $(HOST_DIR)/host_endian.h
 	@mkdir -p $(LIB_DIR)
 	$(call cmd,ln_sf)
 
-.PHONY: $(host_lib) $(graphene_lib) $(pal_lib)
+.PHONY: host_lib_recurse graphene_lib_recurse
 
-$(graphene_lib): $(LIB_DIR)/host_endian.h
+graphene_lib_recurse: $(LIB_DIR)/host_endian.h
 	$(MAKE) -C ../lib target=$(abspath $(LIB_DIR))/
 
-$(host_lib): $(graphene_lib)
+$(graphene_lib): graphene_lib_recurse
+	@true
+
+host_lib_recurse: $(graphene_lib)
 	@[ ! -d host/$(PAL_HOST) ] || $(MAKE) -C host/$(PAL_HOST)
 
+$(host_lib): host_lib_recurse
+	@true
+
 $(pal_loader): $(host_lib)
 
 $(runtime_loader): $(pal_loader)