arch: add BR2_ARCH_NEEDS_GCC_AT_LEAST_8

This new symbol will be used by architectures introduced with gcc 8 and
by external toolchains based on gcc 8.

[1] https://gcc.gnu.org/gcc-8/changes.html

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

arch/Config.in

@@ -282,6 +282,10 @@ config BR2_ARCH_NEEDS_GCC_AT_LEAST_7
 	bool
 	select BR2_ARCH_NEEDS_GCC_AT_LEAST_6
 
+config BR2_ARCH_NEEDS_GCC_AT_LEAST_8
+	bool
+	select BR2_ARCH_NEEDS_GCC_AT_LEAST_7
+
 # The following string values are defined by the individual
 # Config.in.$ARCH files
 config BR2_ARCH