Config.in: require host gcc of at least 8

Ccache 4.9.1 requires a host gcc of at least 8.
See "Build-time support" at
https://ccache.dev/platform-compiler-language-support.html

Signed-off-by: Brandon Maier <brandon.maier@collins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

Config.in

@@ -318,8 +318,12 @@ config BR2_JLEVEL
 	  Number of jobs to run simultaneously. If 0, determine
 	  automatically according to number of CPUs on the host system.
 
+comment "ccache needs a host gcc >= 8"
+	depends on !BR2_HOST_GCC_AT_LEAST_8
+
 config BR2_CCACHE
 	bool "Enable compiler cache"
+	depends on BR2_HOST_GCC_AT_LEAST_8
 	help
 	  This option will enable the use of ccache, a compiler cache.
 	  It will cache the result of previous builds to speed up future