disable IB & SDK when using an external toolchain (closes: #6001)

SVN-Revision: 18837

target/imagebuilder/Config.in

@@ -3,6 +3,7 @@ config IB
 	depends !TARGET_ROOTFS_INITRAMFS
 	depends !TARGET_uml
 	depends !PROFILE_KCONFIG
+	depends !EXTERNAL_TOOLCHAIN
 	select ALL
 	help
 	  This is essentially a stripped-down version of the buildroot

target/sdk/Config.in

@@ -1,5 +1,6 @@
 config SDK
 	bool "Build the OpenWrt SDK"
+	depends !EXTERNAL_TOOLCHAIN
 	help
 	  This is essentially a stripped-down version of the buildroot
 	  with a precompiled toolchain. It can be used to develop and