Fix the MSDOS build

Fix the MSDOS build

* config.bat:
* msdos/sedlisp.inp:
* msdos/sedlibmk.inp:
* msdos/sedleim.inp:
* msdos/sedadmin.inp:
* msdos/sed6.inp:
* msdos/sed3v2.inp:
* msdos/sed2v2.inp:
* msdos/sed1v2.inp: Adapt to Emacs 25.

* src/process.c (remove_slash_colon): Move out of "#ifdef
subprocesses" block, as it its called unconditionally.  Move
ADD_SUBFEATURE calls into "#ifdef subprocesses" block, as they
reference variables only defined in that block.
* src/msdos.h: Provide prototypes for IT_set_frame_parameters,
faccessat, msdos_fatal_signal, syms_of_msdos, pthread_sigmask,
dos_keysns, dos_keyread, run_msdos_command, and
syms_of_win16select, to avoid compiler warnings.
* src/msdos.c (SYS_ENVIRON): Define to either '_environ' or
'environ', depending on the DJGPP version.
Remove declarations of externally-visible Lisp objects, like
Qbackground_color and Qreverse.
(run_msdos_command): First argument is not signed, not unsigned.
Use SYS_ENVIRON.
(sys_select): Use 'timespec_cmp' instead of 'timespec_sign', as
the latter doesn't work when 'time_t' is an unsigned data type.
This caused idle timers to behave incorrectly: they only fired
after a keyboard input event.
* src/frame.c (adjust_frame_size) [MSDOS]: Account for
FRAME_TOP_MARGIN that isn't counted in the frame's number of
lines, but dos_set_window_size needs it to be added.
* src/lread.c (INFINITY, NAN) [DJGPP < 2.05]: Provide definitions.
* src/fns.c (sort_vector_copy) [__GNUC__ < 4]: Provide a prototype
that works around compilation errors with older GCC versions.
* src/w16select.c: Don't declare QCLIPBOARD and QPRIMARY as Lisp
Objects.
* src/filelock.c [MSDOS]: Ifdef away most of the code.  Provide
no-op implementations for 'lock_file' and 'unlock_file'.
(Ffile_locked_p) [MSDOS]: Always return nil.  This avoids multiple
ifdefs in all users of filelock.c functionality.
* src/conf_post.h (EOVERFLOW, SIZE_MAX) [DJGPP < 2.04]: Define.
* src/emacs.c [MSDOS]: Include dosfns.h, to avoid compiler
warnings.
* src/dosfns.h: Provide prototypes for dos_cleanup,
syms_of_dosfns, and init_dosfns.
* src/deps.mk (atimer.o): Depend on msdos.h.
(emacs.o): Depend on dosfns.h.
* src/atimer.c [MSDOS]: Include msdos.h, to avoid compiler
warnings.

* lisp/window.el (window--adjust-process-windows): Skip the body
if 'process-list' is not available.  This avoids failure to start
up on MS-DOS.
* lisp/vc/diff.el (diff-no-select): Test 'make-process', not
'start-process', as the latter is now available on all platforms.
* lisp/textmodes/ispell.el (ispell-async-processp): Replace
'start-process' with 'make-process' in a comment.
* lisp/term/internal.el (IT-unicode-translations): Modify and add
a few translations to display Info files with Unicode markup.  Fix
an ancient off-by-one mismatch error with Unicode codepoints.
* lisp/progmodes/compile.el (compilation-start): Test
'make-process', not 'start-process', as the latter is now
available on all platforms.
* lisp/man.el (Man-build-man-command, Man-getpage-in-background):
Test 'make-process', not 'start-process', as the latter is now
available on all platforms.
* lisp/international/mule-cmds.el (set-coding-system-map): Test
'make-process', not 'start-process', as the latter is now
available on all platforms.
* lisp/eshell/esh-cmd.el (eshell-do-pipelines-synchronously): Doc
fix.
(eshell-execute-pipeline): Test 'make-process', not
'start-process', as the latter is now available on all platforms.