Do not clutter up the Buildroot source directory

...i.e, make sure that we build this pre-init hook within the
per-package build directory.

Change-Id: I1acd1fbe96f174cf22c0522e8c25d2594afcd7e6
diff --git a/package/czechlight-cfg-fs/czechlight-cfg-fs.mk b/package/czechlight-cfg-fs/czechlight-cfg-fs.mk
index 67f2e55..888dc34 100644
--- a/package/czechlight-cfg-fs/czechlight-cfg-fs.mk
+++ b/package/czechlight-cfg-fs/czechlight-cfg-fs.mk
@@ -13,14 +13,14 @@
 endif
 
 define CZECHLIGHT_CFG_FS_BUILD_CMDS
-	$(TARGET_CC) $(BR2_EXTERNAL_CZECHLIGHT_PATH)/package/czechlight-cfg-fs/czechlight-random-seed.c -o czechlight-random-seed
+	$(TARGET_CC) $(CZECHLIGHT_CFG_FS_PKGDIR)/czechlight-random-seed.c -o $(@D)/czechlight-random-seed
 endef
 
 define CZECHLIGHT_CFG_FS_INSTALL_TARGET_CMDS
 	$(INSTALL) -D -m 0755 \
 		$(BR2_EXTERNAL_CZECHLIGHT_PATH)/package/czechlight-cfg-fs/init-czechlight.sh \
 		$(TARGET_DIR)/sbin/init-czechlight.sh
-	$(INSTALL) -D -m 0755 czechlight-random-seed $(TARGET_DIR)/sbin/czechlight-random-seed
+	$(INSTALL) -D -m 0755 $(@D)/czechlight-random-seed $(TARGET_DIR)/sbin/czechlight-random-seed
 	mkdir -p $(TARGET_DIR)/cfg
 	$(ifeq ($(CZECHLIGHT_CFG_FS_PERSIST_SYSREPO),y))
 		mkdir -p $(TARGET_DIR)/usr/lib/systemd/system/multi-user.target.wants/