patch 8.1.2413: cannot update ex_cmdidxs.h on MS-Windows

Problem:    Cannot update ex_cmdidxs.h on MS-Windows.
Solution:   Add build rules and dependencies. (Ken Takata, closes #5337)
diff --git a/src/Make_vms.mms b/src/Make_vms.mms
index f635d56..0a91631 100644
--- a/src/Make_vms.mms
+++ b/src/Make_vms.mms
@@ -765,7 +765,7 @@
 ex_docmd.obj : ex_docmd.c vim.h [.auto]config.h feature.h os_unix.h \
  ascii.h keymap.h term.h macros.h structs.h regexp.h \
  gui.h beval.h [.proto]gui_beval.pro option.h ex_cmds.h proto.h \
- globals.h
+ globals.h ex_cmdidxs.h
 ex_eval.obj : ex_eval.c vim.h [.auto]config.h feature.h os_unix.h \
  ascii.h keymap.h term.h macros.h structs.h regexp.h \
  gui.h beval.h [.proto]gui_beval.pro option.h ex_cmds.h proto.h \