Fix __stdcall placement and function prototype

Fix __stdcall placement and function prototype

MSVC requires __stdcall to be between the functions return value and the
function name, and that the function pointer type is in the form of

    return_type (WINAPI *function_name)(arguments...)

Signed-off-by: Frank Li <redacted>
Signed-off-by: Marius Storm-Olsen <redacted>
Acked-by: Johannes Sixt <redacted>
Signed-off-by: Junio C Hamano <redacted>