Makefile: test if "dot" exists in "<pkg>-graph-depends"

To be able to check the "dot" command availability in
"<pkg>-graph-depends" move the check to the "graph-depends-requirements" rule.
Also don't use a subshell for the exit command to be sure that the error
will be returned by the shell.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Makefile

@@ -673,9 +673,11 @@ graph-build: $(O)/build/build-time.log
 				   --output=$(O)/graphs/build.pie-$(t).$(BR_GRAPH_OUT) \
 				   $(if $(BR2_GRAPH_ALT),--alternate-colors)$(sep))
 
-graph-depends:
+graph-depends-requirements:
 	@dot -? >/dev/null 2>&1 || \
-		(echo "ERROR: The 'dot' program from Graphviz is needed for graph-depends" >&2; exit 1)
+		{ echo "ERROR: The 'dot' program from Graphviz is needed for graph-depends" >&2; exit 1; }
+
+graph-depends: graph-depends-requirements
 	@$(INSTALL) -d $(O)/graphs
 	@cd "$(CONFIG_DIR)"; \
 	$(TOPDIR)/support/scripts/graph-depends $(BR2_GRAPH_DEPS_OPTS) \

package/pkg-generic.mk

@@ -556,7 +556,7 @@ endif
 $(1)-show-depends:
 			@echo $$($(2)_FINAL_DEPENDENCIES)
 
-$(1)-graph-depends:
+$(1)-graph-depends: graph-depends-requirements
 			@$$(INSTALL) -d $$(O)/graphs
 			@cd "$$(CONFIG_DIR)"; \
 			$$(TOPDIR)/support/scripts/graph-depends -p $(1) $$(BR2_GRAPH_DEPS_OPTS) \