amend! Instead of creating Cygwin symlinks, use deep copy by default

Instead of creating Cygwin symlinks, use deep copy by default

The new `winsymlinks` mode `deepcopy` (which is made the default) lets
calls to `symlink()` create (deep) copies of the source file/directory.

This is necessary because unlike Cygwin, MSYS2 does not try to be its
own little ecosystem that lives its life separate from regular Win32
programs: the latter have _no idea_ about Cygwin-emulated symbolic links
(i.e. system files whose contents start with `!<symlink>\xff\xfe` and
the remainder consists of the NUL-terminated, UTF-16LE-encoded symlink
target).

To support Cygwin-style symlinks, the new mode `sysfile` is introduced.

Co-authored-by: Johannes Schindelin <[email protected]>
Co-authored-by: Jeremy Drake <[email protected]>

winsup/cygwin/path.cc

@@ -2160,6 +2160,10 @@ symlink_deepcopy (const char *oldpath, path_conv &win32_newpath)
   tmp_pathbuf tp;
   path_conv win32_oldpath;
 
+  /* **BEGIN** replace this with
+     resolve_symlink_target (oldpath, win32_newpath. win32_oldpath);
+     when rebasing over 5a706ff0fceb83fd1fe7f072fc28a741fdde65f2
+     (probably Cygwin 3.6) */
   /* The symlink target is relative to the directory in which the
      symlink gets created, not relative to the cwd.  Therefore we
      have to mangle the path quite a bit before calling path_conv.*/
@@ -2174,6 +2178,7 @@ symlink_deepcopy (const char *oldpath, path_conv &win32_newpath)
 	      oldpath);
       win32_oldpath.check (absoldpath, PC_SYM_NOFOLLOW, stat_suffixes);
     }
+  /* **END** */
   if (win32_oldpath.error)
     {
       set_errno (win32_oldpath.error);