Merge branch 'js/symlink-windows'

Upstream symbolic link support on Windows from Git-for-Windows.

* js/symlink-windows:
  mingw: special-case index entries for symlinks with buggy size
  mingw: emulate `stat()` a little more faithfully
  mingw: try to create symlinks without elevated permissions
  mingw: add support for symlinks to directories
  mingw: implement basic `symlink()` functionality (file symlinks only)
  mingw: implement `readlink()`
  mingw: allow `mingw_chdir()` to change to symlink-resolved directories
  mingw: support renaming symlinks
  mingw: handle symlinks to directories in `mingw_unlink()`
  mingw: add symlink-specific error codes
  mingw: change default of `core.symlinks` to false
  mingw: factor out the retry logic
  mingw: compute the correct size for symlinks in `mingw_lstat()`
  mingw: teach dirent about symlinks
  mingw: let `mingw_lstat()` error early upon problems with reparse points
  mingw: drop the separate `do_lstat()` function
  mingw: implement `stat()` with symlink support
  mingw: don't call `GetFileAttributes()` twice in `mingw_lstat()`

Author: gitster

compat/mingw-posix.h

@@ -121,10 +121,6 @@ struct utsname {
  * trivial stubs
  */
 
-static inline int readlink(const char *path UNUSED, char *buf UNUSED, size_t bufsiz UNUSED)
-{ errno = ENOSYS; return -1; }
-static inline int symlink(const char *oldpath UNUSED, const char *newpath UNUSED)
-{ errno = ENOSYS; return -1; }
 static inline int fchmod(int fildes UNUSED, mode_t mode UNUSED)
 { errno = ENOSYS; return -1; }
 #ifndef __MINGW64_VERSION_MAJOR
@@ -197,6 +193,8 @@ int setitimer(int type, struct itimerval *in, struct itimerval *out);
 int sigaction(int sig, struct sigaction *in, struct sigaction *out);
 int link(const char *oldpath, const char *newpath);
 int uname(struct utsname *buf);
+int symlink(const char *target, const char *link);
+int readlink(const char *path, char *buf, size_t bufsiz);
 
 /*
  * replacements of existing functions