Fix makefile include order by using sort/wildcard.

The 'include' directive in GNU make supports wildcards, but their
expansion has no defined sort order (GLOB_NOSORT is passed to glob()).
Usually this doesn't matter. However, there is at least one case where
it does make a difference: toolchain/*/*.mk includes both the
definitions of the external toolchain packages and
pkg-toolchain-external.mk, but pkg-toolchain-external.mk must be
included first.

For predictability, use ordered 'include $(sort $(wildcard ...))'
instead of unordered direct 'include */*.mk' everywhere.

Fixes [1] reported by Petr Vorel:

  make: *** No rule to make target 'toolchain-external-custom', needed by '.../build/toolchain-external/.stamp_configured'.  Stop.

[1] http://lists.busybox.net/pipermail/buildroot/2017-November/206969.html

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Tested-by: Petr Vorel <petr.vorel@gmail.com>
[Arnout: also sort the one remaining include, of the external docs]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

(cherry picked from commit b9d2d4cb4e)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Makefile

@@ -483,8 +483,8 @@ include support/dependencies/dependencies.mk
 
 PACKAGES += $(DEPENDENCIES_HOST_PREREQ)
 
-include toolchain/*.mk
-include toolchain/*/*.mk
+include $(sort $(wildcard toolchain/*.mk))
+include $(sort $(wildcard toolchain/*/*.mk))
 
 # Include the package override file if one has been provided in the
 # configuration.
@@ -1071,7 +1071,7 @@ print-version:
 	@echo $(BR2_VERSION_FULL)
 
 include docs/manual/manual.mk
--include $(foreach dir,$(BR2_EXTERNAL_DIRS),$(dir)/docs/*/*.mk)
+-include $(foreach dir,$(BR2_EXTERNAL_DIRS),$(sort $(wildcard $(dir)/docs/*/*.mk)))
 
 .PHONY: $(noconfig_targets)
 

package/gstreamer/gstreamer.mk

@@ -1 +1 @@
-include package/gstreamer/*/*.mk
+include $(sort $(wildcard package/gstreamer/*/*.mk))

package/gstreamer1/gstreamer1.mk

@@ -1 +1 @@
-include package/gstreamer1/*/*.mk
+include $(sort $(wildcard package/gstreamer1/*/*.mk))

toolchain/toolchain-external/toolchain-external.mk

@@ -25,4 +25,4 @@ $(error No prefix selected for external toolchain package $(BR2_PACKAGE_PROVIDES
 endif
 endif
 
-include toolchain/toolchain-external/*/*.mk
+include $(sort $(wildcard toolchain/toolchain-external/*/*.mk))