Makefile: Fix compilation of Windows resource file

Makefile: Fix compilation of Windows resource file

If the git version number consists of less than three period
separated numbers, then the Windows resource file compilation
issues a syntax error:

  $ touch git.rc
  $ make V=1 git.res
  GIT_VERSION = 1.9.rc0
  windres -O coff \
            -DMAJOR=1 -DMINOR=9 -DPATCH=rc0 \
            -DGIT_VERSION="\\\"1.9.rc0\\\"" git.rc -o git.res
  C:\msysgit\msysgit\mingw\bin\windres.exe: git.rc:2: syntax error
  make: *** [git.res] Error 1
  $

Note that -DPATCH=rc0.

The values passed via -DMAJOR=, -DMINOR=, and -DPATCH= are used in
FILEVERSION and PRODUCTVERSION statements, which expect up to four numeric
values. These version numbers are intended for machine consumption. They
are typically inspected by installers to decide whether a file to be
installed is newer than one that exists on the system, but are not used
for much else.

We can be pretty certain that there are no tools that look at these
version numbers, not even the installer of Git for Windows does.
Therefore, to fix the syntax error, fill in only the first two numbers,
which we are guaranteed to find in Git version numbers.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Acked-by: Pat Thoyts <patthoyts@users.sourceforge.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>