modsign: Use extract-cert to process CONFIG_SYSTEM_TRUSTED_KEYS

Fix up the dependencies somewhat too, while we're at it.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/scripts/Makefile b/scripts/Makefile
index 236f683..1b26617 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -16,7 +16,8 @@
 hostprogs-$(BUILD_C_RECORDMCOUNT) += recordmcount
 hostprogs-$(CONFIG_BUILDTIME_EXTABLE_SORT) += sortextable
 hostprogs-$(CONFIG_ASN1)	 += asn1_compiler
-hostprogs-$(CONFIG_MODULE_SIG)	 += sign-file extract-cert
+hostprogs-$(CONFIG_MODULE_SIG)	 += sign-file
+hostprogs-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += extract-cert
 
 HOSTCFLAGS_sortextable.o = -I$(srctree)/tools/include
 HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include