Pass MAKE into external/poppler's configure

...which does some checks about make and could otherwise add some unhelpful
MAKE=make into its Makefiles if it doesn't find a make (so that the following
$(MAKE) step would needlessly fail).

Change-Id: Id8d11ffbc5a09c9f7f61fb12acc2481468746404

external/poppler/ExternalProject_poppler.mk

@@ -18,7 +18,7 @@ $(eval $(call gb_ExternalProject_register_targets,poppler,\
 $(call gb_ExternalProject_get_state_target,poppler,build) :
 	$(call gb_ExternalProject_run,build,\
 		$(if $(filter TRUE,$(DISABLE_DYNLOADING)),CFLAGS="$(CFLAGS) $(gb_VISIBILITY_FLAGS) $(gb_COMPILEROPTFLAGS)" CXXFLAGS="$(CXXFLAGS) $(gb_VISIBILITY_FLAGS) $(gb_COMPILEROPTFLAGS)") \
-		./configure \
+		MAKE=$(MAKE) ./configure \
 			--with-pic \
 			--enable-static \
 			--disable-shared \