toolchain-external: add gcc 9 entry

This patch allows to use an external toolchain based on gcc 9.

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

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

@@ -27,6 +27,7 @@ config BR2_TOOLCHAIN_EXTERNAL_CUSTOM_PREFIX
 
 choice
 	bool "External toolchain gcc version"
+	default BR2_TOOLCHAIN_EXTERNAL_GCC_9   if BR2_ARCH_NEEDS_GCC_AT_LEAST_9
 	default BR2_TOOLCHAIN_EXTERNAL_GCC_8   if BR2_ARCH_NEEDS_GCC_AT_LEAST_8
 	default BR2_TOOLCHAIN_EXTERNAL_GCC_7   if BR2_ARCH_NEEDS_GCC_AT_LEAST_7
 	default BR2_TOOLCHAIN_EXTERNAL_GCC_6   if BR2_ARCH_NEEDS_GCC_AT_LEAST_6
@@ -38,8 +39,13 @@ choice
 	  Set to the gcc version that is used by your external
 	  toolchain.
 
+config BR2_TOOLCHAIN_EXTERNAL_GCC_9
+	bool "9.x"
+	select BR2_TOOLCHAIN_GCC_AT_LEAST_9
+
 config BR2_TOOLCHAIN_EXTERNAL_GCC_8
 	bool "8.x"
+	depends on !BR2_ARCH_NEEDS_GCC_AT_LEAST_9
 	select BR2_TOOLCHAIN_GCC_AT_LEAST_8
 
 config BR2_TOOLCHAIN_EXTERNAL_GCC_7