patch 8.2.3208: dynamic library load error does not mention why it failed

Problem:    Dynamic library load error does not mention why it failed.
Solution:   Add the error message. (Martin Tournoij, closes #8621)
diff --git a/src/terminal.c b/src/terminal.c
index 1f64c8b..98b4600 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -6862,8 +6862,9 @@
     if (!hWinPtyDLL)
     {
 	if (verbose)
-	    semsg(_(e_loadlib), *p_winptydll != NUL ? p_winptydll
-						       : (char_u *)WINPTY_DLL);
+	    semsg(_(e_loadlib),
+		    (*p_winptydll != NUL ? p_winptydll : (char_u *)WINPTY_DLL),
+		    GetWin32Error());
 	return FAIL;
     }
     for (i = 0; winpty_entry[i].name != NULL