Force IO_CACHE work with files larger than 2-4GiB on 32-bit platforms

The support depends on the SIZEOF_OFF_T value, which in turn depends on _FILE_OFFSET_BITS macro.
Most platforms already define the latter as 64 unconditionally:

GNU.cmake:

SET(_FILE_OFFSET_BITS 64)

HP-UX.cmake:

SET(_FILE_OFFSET_BITS 64)

Linux.cmake:

SET(_FILE_OFFSET_BITS 64)

SunOS.cmake:

SET(_FILE_OFFSET_BITS 64)

Windows doesn't but SIZEOF_OFF_T is forced there in my_global.h:

#if defined (_WIN32)

/*

 off_t is 32 bit long. We do not use C runtime functions

 with off_t but native Win32 file IO APIs, that work with

 64 bit offsets.

*/

#undef SIZEOF_OFF_T

#define SIZEOF_OFF_T 8

Same for _APPLE_

For the rest of the platforms the support is unclear.
The purpose of this task is to clarify the support and unify SIZEOF_OFF_T handling.
This will affect IO_CACHE ability to handle large files, and as a consequence, a transaction of a large (>2-4Gib) size when binlog/replication is enabled.