odb: add back git_odb_backend_loose

`git_odb_backend_loose` was erroneously removed during a refactoring;
add it back.

src/libgit2/odb_loose.c

@@ -1204,3 +1204,37 @@ int git_odb__backend_loose(
 	*backend_out = (git_odb_backend *)backend;
 	return 0;
 }
+
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+int git_odb_backend_loose(
+	git_odb_backend **backend_out,
+	const char *objects_dir,
+	git_odb_backend_loose_options *opts)
+{
+	return git_odb__backend_loose(backend_out, objects_dir, opts);
+}
+#else
+int git_odb_backend_loose(
+	git_odb_backend **backend_out,
+	const char *objects_dir,
+	int compression_level,
+	int do_fsync,
+	unsigned int dir_mode,
+	unsigned int file_mode)
+{
+	git_odb_backend_loose_flag_t flags = 0;
+	git_odb_backend_loose_options opts = GIT_ODB_BACKEND_LOOSE_OPTIONS_INIT;
+
+	if (do_fsync)
+		flags |= GIT_ODB_BACKEND_LOOSE_FSYNC;
+
+	opts.flags = flags;
+	opts.compression_level = compression_level;
+	opts.dir_mode = dir_mode;
+	opts.file_mode = file_mode;
+	opts.oid_type = GIT_OID_DEFAULT;
+
+	return git_odb__backend_loose(backend_out, objects_dir, &opts);
+}
+#endif