include/rom.sh: use ccache when building coreboot

ccache now required, in build dependencies

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/rom.sh

@@ -43,6 +43,7 @@ mkpayload_grub()
 
 mkvendorfiles()
 {
+	[ -z "$mode" ] && $dry cook_coreboot_config
 	check_coreboot_utils "$tree"
 	printf "%s\n" "${version%%-*}" > "$srcdir/.coreboot-version" || \
 	    $err "!mk $srcdir .coreboot-version"
@@ -50,6 +51,14 @@ mkvendorfiles()
 	    x_ ./vendor download $target; return 0
 }
 
+cook_coreboot_config()
+{
+	[ -f "$srcdir/.config" ] || return 0
+	printf "CONFIG_CCACHE=y\n" >> "$srcdir/.config" || \
+	    $err "$srcdir/.config: Could not enable ccache"
+	make -C "$srcdir" oldconfig || $err "Could not cook $srcdir/.config"; :
+}
+
 check_coreboot_utils()
 {
 	for util in cbfstool ifdtool; do