Makefile: include mxe-conf as an order-only dep of all packages

Order-only deps have the benefit of guaranteed early execution and not requiring full rebuilds. It isn't a real package, so we don't want an entry in index.html.

Makefile

@@ -49,6 +49,12 @@ PKGS       := $(call set_create,\
 BUILD      := $(shell '$(EXT_DIR)/config.guess')
 PATH       := $(PREFIX)/$(BUILD)/bin:$(PREFIX)/bin:$(PATH)
 
+# All pkgs have (implied) order-only dependencies on MXE_CONF_PKGS.
+# These aren't meaningful to the pkg list in index.html so
+# use a list in case we want to separate autotools, cmake etc.
+MXE_CONF_PKGS := mxe-conf
+PKGS          += $(MXE_CONF_PKGS)
+
 # define some whitespace variables
 define newline
 
@@ -363,7 +369,8 @@ $(PREFIX)/$(3)/installed/$(1): $(TOP_DIR)/src/$(1).mk \
                           $(wildcard $(TOP_DIR)/src/$(1)-test*) \
                           $(addprefix $(PREFIX)/$(3)/installed/,$(value $(call LOOKUP_PKG_RULE,$(1),DEPS,$(3)))) \
                           | $(if $(DONT_CHECK_REQUIREMENTS),,check-requirements) \
-                          $(if $(value $(call LOOKUP_PKG_RULE,$(1),URL,$(3))),download-only-$(1))
+                          $(if $(value $(call LOOKUP_PKG_RULE,$(1),URL,$(3))),download-only-$(1)) \
+                          $(addprefix $(PREFIX)/$(3)/installed/,$(if $(call set_is_not_member,$(1),$(MXE_CONF_PKGS)),$(MXE_CONF_PKGS)))
 	@[ -d '$(LOG_DIR)/$(TIMESTAMP)' ] || mkdir -p '$(LOG_DIR)/$(TIMESTAMP)'
 	$(if $(value $(call LOOKUP_PKG_RULE,$(1),BUILD,$(3))),
 	    @$(PRINTF_FMT) '[build]'    '$(1)' '$(3)',

src/mxe-conf.mk

@@ -0,0 +1,6 @@
+# This file is part of MXE.
+# See index.html for further information.
+
+PKG            := mxe-conf
+$(PKG)_VERSION := 1
+$(PKG)_UPDATE  := echo 1