bug#23163: 25.1.50; w32-lwindow-modifier "unset" while running GDB

[martin rudalics <rudalics@gmx.at>]

In my .emacs for Windows I have for many years the following settings.

(setq w32-pass-lwindow-to-system nil)
(setq w32-lwindow-modifier 'hyper)	; lwindow is hyper
(global-set-key [(control hyper meta b)] 'break-point-insert)

‘break-point-insert’ is a command that inserts a breakpoint into the
*gud-emacs.exe* buffer.  This command works fine in emacs-25 but fails
in master when running GDB.  In particular, it fails _after_ focus has
shifted to the debugged frame and I shifted it back to the debugger
frame.  The command actually executed by C-H-M b is then ‘backward-sexp’
which means that apparently ‘w32-lwindow-modifier’ has been unset and my
modifier given back to the system.

I believe that I have seen similar "unsettings" in other occasions as
well but the example given here is the only one I can confirm.

In GNU Emacs 25.1.50.1 (i686-pc-mingw32)
  of 2016-03-30 built on MACHNO
Repository revision: 292c4753923a468e6c29733ef8701cf2c6680aa8
Windowing system distributor 'Microsoft Corp.', version 5.1.2600
Configured using:
  'configure --prefix=/c/emacs-git/opt CFLAGS=-O3'

martin