Use _LARGE_FILES on AIX

In the same spirit as JDK-8318696, we should adapt the AIX-specific code in hotspot so it uses the well-defined posix <foo> functions, instead of <foo>64. By setting the define _LARGE_FILES, this will make <foo> behave as <foo>64, just as _FILE_OFFSET_BITS=64 does on gcc. (Reference: https://www.ibm.com/docs/en/aix/7.1?topic=volumes-writing-programs-that-access-large-files)

In theory, it should not even be necessary to set this, since we only compile for 64-bit AIX platforms, and this is only relevant on 32-bit platforms. But let's add the define anyway, for good measure. It shows at least that we have thought about the matter. :-)