kbuild: add "cross_tools" target to build tools for the target

Programs in tools/ directory are usually built for the host.
But some of them (mkimage, dumpimge, gen_eth_addr, etc.) are
useful on the target OS too.

Actually, prior to Kbuild, U-Boot could build tools for
the target like follows:

  $ make <target_board>_config
  $ export CROSS_COMPILE=<cross_gcc_prefix>
  $ make HOSTCC=${CROSS_COMPILE}gcc HOSTSTRIP=${CROSS_COMPILE}strip tools

In Kbuild, we can no longer replace HOSTCC at the command line.

In order to get back that feature, this commit adds "cross-tools" target.

Usage:

  Build tools for the host
  $ make CROSS_COMPILE=<cross_gcc_prefix> tools

  Build tools for the target
  $ make CROSS_COMPILE=<cross_gcc_prefix> cross_tools

Besides, "make cross_tools" strip tools programs because we
generally expect smaller storages on embedded systems.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Reported-by: Heiko Schocher <hs@denx.de>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Tom Rini <trini@ti.com>
Tested-by: Heiko Schocher <hs@denx.de>
Acked-by: Heiko Schocher <hs@denx.de>

Makefile

@@ -1155,6 +1155,9 @@ env: scripts_basic
 tools-all: export HOST_TOOLS_ALL=y
 tools-all: env tools ;
 
+cross_tools: export CROSS_BUILD_TOOLS=y
+cross_tools: tools ;
+
 .PHONY : CHANGELOG
 CHANGELOG:
 	git log --no-merges U-Boot-1_1_5.. | \

tools/Makefile

@@ -191,3 +191,15 @@ $(LOGO_DATA_H):	$(obj)/bmp_logo $(LOGO_BMP)
 
 # Let clean descend into subdirs
 subdir- += env
+
+ifneq ($(CROSS_BUILD_TOOLS),)
+HOSTCC = $(CC)
+
+quiet_cmd_crosstools_strip = STRIP   $^
+      cmd_crosstools_strip = $(STRIP) $^; touch $@
+$(obj)/.strip: $(call objectify,$(filter $(always),$(hostprogs-y)))
+	$(call cmd,crosstools_strip)
+
+always += .strip
+endif
+clean-files += .strip