submodule: use absolute path for computing relative path connecting

The current caller of connect_work_tree_and_git_dir passes
an absolute path for the `git_dir` parameter. In the future patch
we will also pass in relative path for `git_dir`. Extend the functionality
of connect_work_tree_and_git_dir to take relative paths for parameters.

We could work around this in the future patch by computing the absolute
path for the git_dir in the calling site, however accepting relative
paths for either parameter makes the API for this function much harder
to misuse.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: stefanbeller

submodule.c

@@ -1223,27 +1223,28 @@ int merge_submodule(unsigned char result[20], const char *path,
 }
 
 /* Update gitfile and core.worktree setting to connect work tree and git dir */
-void connect_work_tree_and_git_dir(const char *work_tree, const char *git_dir)
+void connect_work_tree_and_git_dir(const char *work_tree_, const char *git_dir_)
 {
 	struct strbuf file_name = STRBUF_INIT;
 	struct strbuf rel_path = STRBUF_INIT;
-	const char *real_work_tree = xstrdup(real_path(work_tree));
+	char *git_dir = xstrdup(real_path(git_dir_));
+	char *work_tree = xstrdup(real_path(work_tree_));
 
 	/* Update gitfile */
 	strbuf_addf(&file_name, "%s/.git", work_tree);
 	write_file(file_name.buf, "gitdir: %s",
-		   relative_path(git_dir, real_work_tree, &rel_path));
+		   relative_path(git_dir, work_tree, &rel_path));
 
 	/* Update core.worktree setting */
 	strbuf_reset(&file_name);
 	strbuf_addf(&file_name, "%s/config", git_dir);
 	git_config_set_in_file(file_name.buf, "core.worktree",
-			       relative_path(real_work_tree, git_dir,
-					     &rel_path));
+			       relative_path(work_tree, git_dir, &rel_path));
 
 	strbuf_release(&file_name);
 	strbuf_release(&rel_path);
-	free((void *)real_work_tree);
+	free(work_tree);
+	free(git_dir);
 }
 
 int parallel_submodules(void)