gcc/libmudflap: also unavailable for gcc 6.x

libmudflap was removed in gcc 4.9:
https://gcc.gnu.org/wiki/Mudflap_Pointer_Debugging

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gcc/Config.in.host

@@ -153,6 +153,7 @@ config BR2_GCC_ENABLE_LIBMUDFLAP
 	depends on !BR2_ARM_INSTRUCTIONS_THUMB && !BR2_powerpc_SPE
 	depends on !BR2_GCC_VERSION_4_9_X
 	depends on !BR2_GCC_VERSION_5_X
+	depends on !BR2_GCC_VERSION_6_X
 	help
 	  libmudflap is a gcc library used for the mudflap pointer
 	  debugging functionality. It is only needed if you intend to