repo: Delete compat files with commit

Like the detached metadata, delete the compat sizes and signature files
if they exist when deleting a commit object.

[endlessm/eos-shell#5083]

Rebase 2016.9: Switch to glnx_set_error_from_errno
Rebase 2016.15 (T14427): Merge error conditions to single check and
  prefix the error with the failed file
Rebase 2017.12 (T18936): Rework to use ot_ensure_unlinked_at()
Rebase 2018.4 (T17367, T22022): Inline compat file loose path calculation

src/libostree/ostree-repo.c

@@ -4260,6 +4260,26 @@ ostree_repo_delete_object (OstreeRepo           *self,
 
       if (!ot_ensure_unlinked_at (self->objects_dir_fd, meta_loose, error))
         return FALSE;
+
+      /* Delete optional compat objects */
+      const char compat_files_exts[][7] = { "sig", "sizes2" };
+      for (gsize i = 0; i < G_N_ELEMENTS (compat_files_exts); i++)
+        {
+          const char *ext = compat_files_exts[i];
+          char *buf = meta_loose;
+
+          /* Write the compat object loose name manually since there's no
+           * loose path API that handles arbitrary file extensions
+           */
+          *buf = sha256[0];
+          buf++;
+          *buf = sha256[1];
+          buf++;
+          snprintf (buf, _OSTREE_LOOSE_PATH_MAX - 2, "/%s.%s", sha256 + 2, ext);
+
+          if (!ot_ensure_unlinked_at (self->objects_dir_fd, meta_loose, error))
+            return FALSE;
+        }
     }
 
   if (!glnx_unlinkat (self->objects_dir_fd, loose_path, 0, error))