tools/env: cross-compile fw_printenv without setting HOSTCC

fw_printenv is a program which mostly runs on the target Linux.

Before switching to Kbuild, we needed to set HOSTCC at the
command line like this:
    make HOSTCC=<your CC cross-compiler> env

Going forward we can cross compile it by specifying CROSS_COMPILE:
    make CROSS_COMPILE=<your cross-compiler prefix> env
This looks more natural.
Signed-off-by: NMasahiro Yamada <yamada.m@jp.panasonic.com>
Tested-by: NGerhard Sittig <gsi@denx.de>

tools/.gitignore

@@ -16,7 +16,6 @@
 /xway-swap-bytes
 /*.exe
 /easylogo/easylogo
-/env/fw_printenv
 /gdb/gdbcont
 /gdb/gdbsend
 /kernel-doc/docproc

tools/env/.gitignore

+fw_printenv
+fw_printenv_unstripped

tools/env/Makefile

@@ -5,6 +5,11 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
+# fw_printenv is supposed to run on the target system, which means it should be
+# built with cross tools. Although it may look weird, we only replace "HOSTCC"
+# with "CC" here for the maximum code reuse of scripts/Makefile.host.
+HOSTCC = $(CC)
+
 # Compile for a hosted environment on the target
 HOST_EXTRACFLAGS  = $(patsubst -I%,-idirafter%, $(UBOOTINCLUDE)) \
 		-idirafter $(SRCTREE)/tools/env \
@@ -15,9 +20,15 @@ ifeq ($(MTD_VERSION),old)
 HOST_EXTRACFLAGS += -DMTD_OLD
 endif
 
-hostprogs-y := fw_printenv
-always := $(hostprogs-y)
+always := fw_printenv
+hostprogs-y := fw_printenv_unstripped
 
-fw_printenv-objs := fw_env.o fw_env_main.o \
+fw_printenv_unstripped-objs := fw_env.o fw_env_main.o \
 	crc32.o ctype.o linux_string.o \
 	env_attr.o env_flags.o
+
+quiet_cmd_strip = STRIP   $@
+      cmd_strip = $(STRIP) -o $@ $<
+
+$(obj)/fw_printenv: $(obj)/fw_printenv_unstripped FORCE
+	$(call if_changed,strip)

tools/env/README

@@ -2,11 +2,10 @@
 This is a demo implementation of a Linux command line tool to access
 the U-Boot's environment variables.
 
-In the current version, there is an issue in cross-compilation.
 In order to cross-compile fw_printenv, run
-    make HOSTCC=<your CC cross-compiler> env
+    make CROSS_COMPILE=<your cross-compiler prefix> env
 in the root directory of the U-Boot distribution. For example,
-    make HOSTCC=arm-linux-gcc env
+    make CROSS_COMPILE=arm-linux- env
 
 For the run-time utility configuration uncomment the line
 #define CONFIG_FILE  "/etc/fw_env.config"