Allows long long integer types in your program.
The default with xlc , xlC and cc is -qlonglong, which defines _LONG_LONG (long long types will work in programs). The default with c89 is -qnolonglong (long long types are not supported).
This option cannot be specified when the selected language level is
stdc99 or extc99. It is used to control the long
long support that is provided as an extension to the C89 standard. This
extension is slightly different from the long long support that is part of the
C99 standard.
xlc myprogram.c -qnolonglong