Support configuring Busybox from _defconfig files

The existing test .config files are moved to configs/ and renamed
to *_defconfig. 'make xyz_defconfig' will enable the
configuration in that specific file.

Signed-off-by: Daniel Fandrich <dan@coneharvesters.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

INSTALL

@@ -70,7 +70,9 @@ create a known starting point.
 Other starting configurations (mostly used for testing purposes) include
 "make allbareconfig" (enables all applets but disables all optional features),
 "make allyesconfig" (enables absolutely everything including debug features),
-and "make randconfig" (produce a random configuration).
+and "make randconfig" (produce a random configuration).  The configs/ directory
+contains a number of additional configuration files ending in _defconfig which
+are useful in specific cases.  "make help" will list them.
 
 Configuring BusyBox produces a file ".config", which can be saved for future
 use.  Run "make oldconfig" to bring a .config file from an older version of

Makefile

@@ -1042,7 +1042,7 @@ rpm: FORCE
 # Brief documentation of the typical targets used
 # ---------------------------------------------------------------------------
 
-boards := $(wildcard $(srctree)/arch/$(ARCH)/configs/*_defconfig)
+boards := $(wildcard $(srctree)/configs/*_defconfig)
 boards := $(notdir $(boards))
 
 -include $(srctree)/Makefile.help
@@ -1131,15 +1131,6 @@ clean: $(clean-dirs)
 		-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \) \
 		-type f -print | xargs rm -f
 
-help:
-	@echo  '  Building external modules.'
-	@echo  '  Syntax: make -C path/to/kernel/src M=$$PWD target'
-	@echo  ''
-	@echo  '  modules         - default target, build the module(s)'
-	@echo  '  modules_install - install the module'
-	@echo  '  clean           - remove generated files in module directory only'
-	@echo  ''
-
 # Dummies...
 PHONY += prepare scripts
 prepare: ;

Makefile.help

@@ -25,6 +25,10 @@ help:
 	@echo '  			  You can use these commands if the commands on the host'
 	@echo '  			  is unusable. Afterwards use it like:'
 	@echo '  			  make SED="$(objtree)/sed"'
+	@$(if $(boards), \
+		$(foreach b, $(boards), \
+		printf "  %-21s - Build for %s\\n" $(b) $(subst _defconfig,,$(b));) \
+		echo '')
 	@echo
 	@echo 'Installation:'
 	@echo '  install		- install busybox into CONFIG_PREFIX'

scripts/kconfig/Makefile

@@ -87,7 +87,7 @@ endif
 	$(MTIME_IS_COARSE) && sleep 1
 
 %_defconfig: $(obj)/conf
-	$(Q)$< -D $@ Config.in
+	$(Q)$< -D configs/$@ Config.in
 	$(MTIME_IS_COARSE) && sleep 1
 
 # Help text used by make help