msvc: Fix build by adding missing INTMAX_MAX define

Commit c03c831 (do not depend on signed integer overflow, 05-10-2010) provokes an msvc build failure. The cause of the failure is a missing definition of the INTMAX_MAX constant, used in the new maximum_signed_value_of_type(a) macro, which would normally be defined in the C99 <stdint.h> header file. In order the fix the compilation error, we add an appropriate definition of the INTMAX_MAX constant, along with INTMAX_MIN and UINTMAX_MAX, to an msvc compat header file. 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>