mingw: Try to delete target directory first.

When the rename function tries to move a directory it fails if the target
directory exists. It should check if it can delete the (possibly empty)
target directory and then try again to move the directory.

Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: 마누엘 <nalla@users.noreply.github.com>

compat/mingw.c

@@ -1648,7 +1648,12 @@ repeat:
 	if (gle == ERROR_ACCESS_DENIED &&
 	    (attrs = GetFileAttributesW(wpnew)) != INVALID_FILE_ATTRIBUTES) {
 		if (attrs & FILE_ATTRIBUTE_DIRECTORY) {
-			errno = EISDIR;
+			DWORD attrsold = GetFileAttributesW(wpold);
+			if (attrsold == INVALID_FILE_ATTRIBUTES ||
+			    !(attrsold & FILE_ATTRIBUTE_DIRECTORY))
+				errno = EISDIR;
+			else if (!_wrmdir(wpnew))
+				goto repeat;
 			return -1;
 		}
 		if ((attrs & FILE_ATTRIBUTE_READONLY) &&