grub2: Generate config from pending deployment

Generate a grub2 config using the pending deployment, if a grub2
bootloader is detected in the sysroot. Allows grub2-mkconfig
to run if there are no previous deployments.

Fixes: #1774

Closes: #1831
Approved by: jlebon

src/libostree/ostree-bootloader-syslinux.c

@@ -108,10 +108,11 @@ append_config_from_loader_entries (OstreeBootloaderSyslinux  *self,
 }
 
 static gboolean
-_ostree_bootloader_syslinux_write_config (OstreeBootloader          *bootloader,
-                                          int                    bootversion,
-                                          GCancellable          *cancellable,
-                                          GError               **error)
+_ostree_bootloader_syslinux_write_config (OstreeBootloader  *bootloader,
+                                          int                bootversion,
+                                          GPtrArray         *new_deployments,
+                                          GCancellable      *cancellable,
+                                          GError           **error)
 {
   OstreeBootloaderSyslinux *self = OSTREE_BOOTLOADER_SYSLINUX (bootloader);