This article is from the FAQ, by with numerous contributions by others.
When the beta compiler is used on IRIX 5.3 it may give the warning ld:
WARNING 56: Invalid warning number (133) at link time. This warning is
caused by the compiler trying to turn of an IRIX 6.2 warning (number 133),
which does not exist on IRIX 5.3. The warning can be safely ignored.