enablke ccache on kernel compile

eclass/sablink-kernel.eclass

@@ -403,6 +403,7 @@ else
 		sys-devel/autoconf
 		sys-devel/make
 		sys-fs/dosfstools
+		dev-util/ccache
 		|| ( >=sys-kernel/genkernel-next-5 >=sys-kernel/genkernel-3.4.45-r2 )
 		arm? ( dev-embedded/u-boot-tools sys-block/devio )
 		amd64? ( sys-apps/v86d )
@@ -776,6 +777,7 @@ _kernel_src_compile() {
 		--bootdir="${WORKDIR}"/boot \
 		--mountboot \
 		--module-prefix="${WORKDIR}"/lib \
+		--kernel-cc=/usr/lib/ccache/bin/${CHOST}-gcc \
 		all || die "genkernel failed"
 
 	if [ -n "${K_MKIMAGE_KERNEL_ADDRESS}" ]; then