bug#19989: 25.0.50; Build instructions on Windows

[Ilya Zakharevich <nospam-abuse@ilyaz.org>]

=======================================================

I needed the following changes to build Emacs (when following the
instructions in nt/INSTALL):
  • mingw-get:
	actually, mingw32-base is not installed by default;
        I needed to install it by manually marking it in mingw-get.
  • mingw shell sets path to (essentially) FOO/msys/1.0/mingw/bin (here FOO
        is the install path), but there is no directory
          FOO/msys/1.0/mingw
        what is is
          FOO/bin
    So I needed to make a symbolic link (Windows style required) by
    running
        mklink /j mingw FOO
    in FOO/msys/1.0

=======================================================



In GNU Emacs 25.0.50.20 (i686-pc-mingw32)
 of 2015-02-08 on BUCEFAL
Repository revision: d5e3922e08587e7eb9e5aec2e9f84cbda405f857
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/k/test'

Configured features:
SOUND NOTIFY ACL

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1252

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message dired format-spec
rfc822 mml easymenu mml-sec mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util help-fns mail-prsvr mail-utils time-date tooltip
eldoc electric uniquify ediff-hook vc-hooks lisp-float-type mwheel
dos-w32 ls-lisp disp-table w32-win w32-vars tool-bar dnd fontset image
regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese case-table epa-hook jka-cmpr-hook help simple abbrev
minibuffer cl-preloaded nadvice loaddefs button faces cus-face macroexp
files text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
w32notify w32 multi-tty emacs)

Memory information:
((conses 8 80324 9864)
 (symbols 32 17968 0)
 (miscs 32 85 128)
 (strings 16 12688 4007)
 (string-bytes 1 324435)
 (vectors 8 9470)
 (vector-slots 4 390690 6074)
 (floats 8 65 62)
 (intervals 28 243 45)
 (buffers 516 13))