toolchain/toolchain-external/toolchain-external-custom: add gcc 13 version selection

This patch allows to use an external toolchain based on gcc 13.

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

toolchain/toolchain-external/toolchain-external-custom/Config.in.options

@@ -46,6 +46,10 @@ choice
 	  Set to the gcc version that is used by your external
 	  toolchain.
 
+config BR2_TOOLCHAIN_EXTERNAL_GCC_13
+	bool "13.x"
+	select BR2_TOOLCHAIN_GCC_AT_LEAST_13
+
 config BR2_TOOLCHAIN_EXTERNAL_GCC_12
 	bool "12.x"
 	select BR2_TOOLCHAIN_GCC_AT_LEAST_12