Introduce ensure_all custom function

Some targets require the image partition to be mounted.
Although, it is easy to detect this (and mount the partition)
by depending on the phony target image_mount_if, make is unable
to calculate the dependencies correctly. The reason is that some
dependencies are located on the partition (which is not mounted
when scanning for dependencies). Hence, make will rebuild all
targets (after it mounted the partition) regardless of the state
of these files.

To solve this issue we introduce ensure_mount and call it on phony
targets invoked by the user. The actual target will be converted and
serve as wrapper which mounts the partition and then invokes the actual
target renamed to <name>__ignore_mount.

Makefile

@@ -48,6 +48,37 @@ define to_arch =
 $(if $(subst amd64,,$1),$(if $(subst i386,,$1),$1,i686),x86_64)
 endef
 
+#Some targets require the image partition to be mounted.
+#Although, it is easy to detect this (and mount the partition)
+#by depending on the phony target image_mount_if, make is unable
+#to calculate the dependencies correctly. The reason is that some
+#dependencies are located on the partition (which is not mounted
+#when scanning for dependencies). Hence, make will rebuild all
+#targets (after it mounted the partition) regardless of the state
+#of these files.
+#
+#To solve this issue we call ensure_mount on phony targets invoked
+#by the user. The actual target will serve as a wrapper which
+#mounts the partition and then invokes the actual target renamed
+#to <name>__ignore_mount. Note that both targets will be marked
+#as phony, since the renaming makes no sense for files (and most
+#probably this is a file on the partition anyway...) and the user
+#will invoke a phony target anyway.
+#
+#tl;dr every target that requires the image partition to be mounted
+#should be encapsulated in $(call ensure_mount,<target_name>).
+#
+#Finally, do not change _any_ whitespaces in the defintion of
+#ensure_mount without knowing exactly what you are doing. This is
+#dark magic!
+define ensure_mount =
+$(eval
+.PHONY : $(strip $1) $(strip $1)__ignore_mount
+$(strip $1): image_mount_if
+	$(MAKE) $(strip $1)__ignore_mount
+)$(strip $1)__ignore_mount
+endef
+
 RSYNC=rsync -a
 LZMA_FLAGS=-T 0