Problem: MS-Windows: dealing with deprecation is too complicated.
Solution: Use io.h directly. Move _CRT_SECURE_NO_DEPRECATE to the build
file. Suppress C4091 warning by setting "_WIN32_WINNT". (Ken
Takata, closes#5626)
Problem: Alloc() returning "char_u *" causes a lot of type casts.
Solution: Have it return "void *". (Mike Williams) Define ALLOC_ONE() to
check the simple allocations.
Problem: Using "int" for alloc() often results in compiler warnings.
Solution: Use "size_t" and remove type casts. Remove alloc_check(), Vim
only works with 32 bit ints anyway.
Problem: Macros for MS-Windows are inconsistent, using "32", "3264 and
others.
Solution: Use MSWIN for all MS-Windows builds. Use FEAT_GUI_MSWIN for the
GUI build. (Hirohito Higashi, closes#3932)
Problem: Clipboard does not work on Win32 when compiled with Cygwin.
Solution: Move the Win32 clipboard code to a separate file and use it when
building with os_unix.c. (Frodak Baksik, Ken Takata)
