msvc: git-daemon.exe: Fix linker "unresolved externals" error

msvc: git-daemon.exe: Fix linker "unresolved externals" error

The msvc linker complains about external symbols referenced by
the new poll() emulation code. In particular, it complains about
the DispatchMessage(), PeekMessage(), TranslateMessage() and
MsgWaitForMultipleObjects() functions.

In order to satisfy the external references, we link against the
user32.lib library.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Acked-by: Erik Faye-Lund <kusmabite@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>