package/linux-tools: change method for including linux-tool sub-makefiles

Make inclusion ordering of all linux-tool-*.mk sub-makefiles explicit
instead of relying on alphabetical sort order. This is done by
renaming the Linux tools sub-makefiles to the format linux-tool-*.mk.in.
This causes the top-level Makefile to ignore the Linux tools
sub-makefiles.

Until now, the main Makefile included all linux-tool-*.mk files, as
well as linux-tools.mk, and it relied on alphabetical sorting to
include them in the proper order (linux-tool-*.mk before
linux-tools.mk).

Signed-off-by: Markus Mayer <mmayer@broadcom.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
[Thomas: improve comment in the code as suggested by Yann.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/manual/adding-packages-linux-kernel-spec-infra.txt

@@ -40,8 +40,8 @@ Unlike other packages, the +linux-tools+ package options appear in the
 +linux+ kernel menu, under the `Linux Kernel Tools` sub-menu, not under
 the `Target packages` main menu.
 
-Then for each linux tool, add a new +.mk+ file named
-+package/linux-tools/linux-tool-foo.mk+. It would basically look like:
+Then for each linux tool, add a new +.mk.in+ file named
++package/linux-tools/linux-tool-foo.mk.in+. It would basically look like:
 
 ------------------------------
 01: ################################################################################

package/linux-tools/linux-tools.mk

@@ -10,15 +10,14 @@
 #
 # So, all tools refer to $(LINUX_DIR) instead of $(@D).
 
-# Note: we need individual tools .mk files to be included *before* this one
-# to guarantee that each tool has a chance to register itself before we build
-# the list of build and install hooks, below.
-#
-# This is currently guaranteed by the naming of each file:
-# - they get included by the top-level Makefile, with $(sort $(wildcard ...))
-# - make's $(sort) function will aways sort in the C locale
-# - the files names correctly sort out in the C locale so that each tool's
-#   .mk file is included before this one.
+# Note: we need individual tools makefiles to be included *before* we build
+# the list of build and install hooks below to guarantee that each tool has
+# a chance to register itself once, and only once. Therefore, the makefiles
+# are named linux-tool-*.mk.in, so they won't be picked up by the top-level
+# Makefile, but can be included here, guaranteeing the single inclusion and
+# the proper ordering.
+
+include $(sort $(wildcard package/linux-tools/*.mk.in))
 
 # We only need the kernel to be extracted, not actually built
 LINUX_TOOLS_PATCH_DEPENDENCIES = linux