busybox: alternatives: accomodate CONFIG_BUSYBOX_CUSTOM=y

When busybox customisation is enabled, we should depend on config
symbols CONFIG_BUSYBOX_CONFIG_xxx to form alternatives specs

Reported-by: Hannu Nyman <hannu.nyman@iki.fi>
Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

package/utils/busybox/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=busybox
 PKG_VERSION:=1.26.2
-PKG_RELEASE:=6
+PKG_RELEASE:=7
 PKG_FLAGS:=essential
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
@@ -36,6 +36,9 @@ else
   BB_MAKE_VERBOSE :=
 endif
 
+BUSYBOX_SYM=$(if $(CONFIG_BUSYBOX_CUSTOM),CONFIG,DEFAULT)
+BUSYBOX_IF_ENABLED=$(if $(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_$(1)),$(2))
+
 define Package/busybox
   SECTION:=base
   CATEGORY:=Base system
@@ -45,17 +48,17 @@ define Package/busybox
   DEPENDS:=+BUSYBOX_USE_LIBRPC:librpc +BUSYBOX_CONFIG_PAM:libpam +BUSYBOX_CONFIG_NTPD:jsonfilter
   MENU:=1
   ALTERNATIVES:=\
-    $(if $(CONFIG_BUSYBOX_DEFAULT_KILL),	100:/bin/kill:/bin/busybox) \
-    $(if $(CONFIG_BUSYBOX_DEFAULT_PS),		100:/bin/ps:/bin/busybox) \
-    $(if $(CONFIG_BUSYBOX_DEFAULT_WATCH),	100:/bin/watch:/bin/busybox) \
-    $(if $(CONFIG_BUSYBOX_DEFAULT_IP),		100:/sbin/ip:/bin/busybox) \
-    $(if $(CONFIG_BUSYBOX_DEFAULT_FREE),	100:/usr/bin/free:/bin/busybox) \
-    $(if $(CONFIG_BUSYBOX_DEFAULT_PGREP),	100:/usr/bin/pgrep:/bin/busybox) \
-    $(if $(CONFIG_BUSYBOX_DEFAULT_PKILL),	100:/usr/bin/pkill:/bin/busybox) \
-    $(if $(CONFIG_BUSYBOX_DEFAULT_PMAP),	100:/usr/bin/pmap:/bin/busybox) \
-    $(if $(CONFIG_BUSYBOX_DEFAULT_PWDX),	100:/usr/bin/pwdx:/bin/busybox) \
-    $(if $(CONFIG_BUSYBOX_DEFAULT_TOP),		100:/usr/bin/top:/bin/busybox) \
-    $(if $(CONFIG_BUSYBOX_DEFAULT_UPTIME),	100:/usr/bin/uptime:/bin/busybox) \
+    $(call BUSYBOX_IF_ENABLED,KILL,	100:/bin/kill:/bin/busybox) \
+    $(call BUSYBOX_IF_ENABLED,PS,	100:/bin/ps:/bin/busybox) \
+    $(call BUSYBOX_IF_ENABLED,WATCH,	100:/bin/watch:/bin/busybox) \
+    $(call BUSYBOX_IF_ENABLED,IP,	100:/sbin/ip:/bin/busybox) \
+    $(call BUSYBOX_IF_ENABLED,FREE,	100:/usr/bin/free:/bin/busybox) \
+    $(call BUSYBOX_IF_ENABLED,PGREP,	100:/usr/bin/pgrep:/bin/busybox) \
+    $(call BUSYBOX_IF_ENABLED,PKILL,	100:/usr/bin/pkill:/bin/busybox) \
+    $(call BUSYBOX_IF_ENABLED,PMAP,	100:/usr/bin/pmap:/bin/busybox) \
+    $(call BUSYBOX_IF_ENABLED,PWDX,	100:/usr/bin/pwdx:/bin/busybox) \
+    $(call BUSYBOX_IF_ENABLED,TOP,	100:/usr/bin/top:/bin/busybox) \
+    $(call BUSYBOX_IF_ENABLED,UPTIME,	100:/usr/bin/uptime:/bin/busybox) \
 
 endef
 
@@ -68,8 +71,6 @@ define Package/busybox/config
 	source "$(SOURCE)/Config.in"
 endef
 
-BUSYBOX_SYM=$(if $(CONFIG_BUSYBOX_CUSTOM),CONFIG,DEFAULT)
-
 # don't create a version string containing the actual timestamp
 export KCONFIG_NOTIMESTAMP=1