bug#14503: 24.3.50; MSYS out-of-tree build fails

[Richard Copley <rcopley@gmail.com>]

Building Emacs on Windows according to nt/INSTALL.MSYS,
outside the source tree as recommended, "make -k bootstrap"
fails while processing {build_dir}/lib/Makefile, with the errors:

make[2]: Entering directory `/c/emacs/build/lib'
make[2]: *** No rule to make target `alloca.in.h', needed by `alloca.h'.
make[2]: *** No rule to make target `errno.in.h', needed by `errno.h'.
make[2]: *** No rule to make target `execinfo.in.h', needed by `execinfo.h'.
make[2]: *** No rule to make target `getopt.in.h', needed by `getopt.h'.

Note that the prerequisites are at {trunk}/lib/alloca.in.h, etc.
All seems to work fine if I build inside the source tree.

In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-05-29 on 57172UHB
Bzr revision: 112768 rgm@gnu.org-20130529071809-s1x95w8thdhvjdc1
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix c:/emacs/emacs-112768 CPPFLAGS='-I G:/usr/include
 -I C:/GnuWin32/include' LDFLAGS='-L G:/usr/lib -L C:/GnuWin32/lib''

Important settings:
  value of $LANG: ENG
  locale-coding-system: cp1252
  default enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
M-x r - e - b <return>

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

Load-path shadows:
None found.

Features:
(shadow sort nadvice gnus-util mail-extr emacsbug message 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 mail-prsvr mail-utils time-date tooltip ediff-hook
vc-hooks lisp-float-type mwheel dos-w32 ls-lisp w32-common-fns
disp-table w32-win w32-vars tool-bar dnd fontset image regexp-opt fringe
tabulated-list newcomment lisp-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 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)