MSVC: link dynamically to the CRT

MSVC: link dynamically to the CRT

Dynamic linking is generally preferred over static linking, and MSVCRT.dll
has been integral part of Windows for a long time.

This also fixes linker warnings for _malloc and _free in zlib.lib, which
seems to be compiled for MSVCRT.dll already.

The DLL version also exports some of the CRT initialization functions,
which are hidden in the static libcmt.lib (e.g. __wgetmainargs, required by
subsequent Unicode patches).

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Stepan Kasal <kasal@ucw.cz>
Acked-by: Sebastian Schuberth <sschuberth@gmail.com>
Acked-by: Marat Radchenko <marat@slonopotamus.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>