gcc: disallow 4.8.x for ARMv8 cores

Notice: A53/A57 were in fact supported in aarch64 mode in 4.8 (in aarch32
mode only from 4.9), but it doesn't handle --with-abi, and as there is
unlikely to be any aarch64 based legacy projects unwilling to use a newer
GCC version it is simpler to disallow it for all modes.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gcc/Config.in.host

@@ -13,7 +13,7 @@ choice
 		depends on !BR2_microblaze && !BR2_arc \
 			&& !BR2_powerpc64le && !BR2_nios2 && !BR2_bfin
 		# Broken or unsupported ARM cores
-		depends on !BR2_cortex_a12 && !BR2_cortex_a17
+		depends on !BR2_cortex_a12 && !BR2_cortex_a17 && !BR2_ARM_CPU_ARMV8
 		# Broken or unsupported PPC cores
 		depends on !BR2_powerpc_power8
 		# Unsupported MIPS cores