Merge branch 'jk/config-warn-on-inaccessible-paths'

When looking for $HOME/.gitconfig etc., it is OK if we cannot read
them because they do not exist, but we did not diagnose existing
files that we cannot read.

* jk/config-warn-on-inaccessible-paths:
  warn_on_inaccessible(): a helper to warn on inaccessible paths
  attr: warn on inaccessible attribute files
  gitignore: report access errors of exclude files
  config: warn on inaccessible files

git-compat-util.h

@@ -609,6 +609,12 @@ int rmdir_or_warn(const char *path);
  */
 int remove_or_warn(unsigned int mode, const char *path);
 
+/* Call access(2), but warn for any error besides ENOENT. */
+int access_or_warn(const char *path, int mode);
+
+/* Warn on an inaccessible file that ought to be accessible */
+void warn_on_inaccessible(const char *path);
+
 /* Get the passwd entry for the UID of the current process. */
 struct passwd *xgetpwuid_self(void);