arch/Config.in: disable internal toolchain backend for csky

We are going to remove the gcc fork for csky, first disable
the internal toolchain backend.

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Guo Ren <ren_guo@c-sky.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Asked-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

arch/Config.in

@@ -77,6 +77,7 @@ config BR2_aarch64_be
 
 config BR2_csky
 	bool "csky"
+	select BR2_ARCH_HAS_NO_TOOLCHAIN_BUILDROOT
 	select BR2_ARCH_HAS_MMU_MANDATORY
 	# Most variants are supported by gcc-9+, except one that is
 	# handled as a special exception in package/gcc/Config.in.host