Add support for custom post-build script

The config help text says it all:

  Specify a script to be run after the build has finished and before
  the BR2 starts packing the files into selected packages.

  This gives users the oportunity to do board-specific cleanups,
  add-ons and the like, so the generated files can be used directly
  without further processing.

  The script is called with the target directory name as first and
  only argument. Make sure the exit code of that script is 0,
  otherwise make will stop after calling it.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Sven Neumann <s.neumann@raumfeld.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

Makefile

@@ -363,6 +363,10 @@ endif
 	find $(TARGET_DIR) -type f -perm +111 | xargs $(STRIPCMD) 2>/dev/null || true
 	$(TARGET_LDCONFIG) -r $(TARGET_DIR) 2>/dev/null
 
+ifneq ($(BR2_ROOTFS_POST_BUILD_SCRIPT),"")
+	$(BR2_ROOTFS_POST_BUILD_SCRIPT) $(TARGET_DIR)
+endif
+
 ifeq ($(BR2_ENABLE_LOCALE_PURGE),y)
 LOCALE_WHITELIST=$(PROJECT_BUILD_DIR)/locales.nopurge
 LOCALE_NOPURGE=$(strip $(subst ",,$(BR2_ENABLE_LOCALE_WHITELIST)))

target/Config.in

@@ -12,6 +12,21 @@ config BR2_ROOTFS_SUFFIX
 	help
 	  Add a custom string to the end of the root file system name.
 
+config BR2_ROOTFS_POST_BUILD_SCRIPT
+	string "Custom script to run before packing files"
+	default ""
+	help
+	  Specify a script to be run after the build has finished and before
+	  the BR2 starts packing the files into selected packages.
+
+	  This gives users the oportunity to do board-specific cleanups,
+	  add-ons and the like, so the generated files can be used directly
+	  without further processing.
+
+	  The script is called with the target directory name as first and
+	  only argument. Make sure the exit code of that script is 0,
+	  otherwise make will stop after calling it.
+
 comment "filesystem for target device"
 
 source "target/cramfs/Config.in"