meson: define _FILE_OFFSET_BITS=64 for MinGW. See #1476
meson: define _FILE_OFFSET_BITS=64 for MinGW. See #1476

The autotools build set it by default and we use off_t in various places,
even on Windows. Also set it with the meson build to avoid any regressions.

Ideally we shouldn't use off_t and use 64bit capable API on Windows instead, so
we get large file support with MSVC as well.

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib