minstall: Don't treat symlinks to directories as directories in do_copydir()

As documented in https://docs.python.org/3/library/os.html#os.walk:

> dirnames is a list of the names of the subdirectories in dirpath
> (including symlinks to directories, and excluding '.' and '..')

So currently, we treat any symlink to a directory as a directory instead
of as a symlink. In practice, this means symlinks to directories are
installed as empty directories instead of as symlinks.

Let's make sure the symlinks are kept intact by checking for symlinks
when we iterate over the directory names and treating any symlinks we
find as files instead of as symlinks.

Author: DaanDeMeyer

mesonbuild/minstall.py

@@ -507,6 +507,9 @@ def do_copydir(self, data: InstallData, src_dir: str, dst_dir: str,
                 abs_src = os.path.join(root, d)
                 filepart = os.path.relpath(abs_src, start=src_dir)
                 abs_dst = os.path.join(dst_dir, filepart)
+                if os.path.islink(abs_src):
+                    files.append(d)
+                    continue
                 # Remove these so they aren't visited by os.walk at all.
                 if filepart in exclude_dirs:
                     dirs.remove(d)