[Predef-contribute] HP C on Itanium

[mal c. <art...@go...>]

Hello.

HP C and aCC define '__ia64' to be '1' on Itanium. It's on the HP C manual page:

      -Dname=def
      -Dname         Define the preprocessor symbol name, as if by
                     '#define'.
                     NOTE: __ia64 and __HP_aCC are defined automatically for
                     aCC and __HP_cc for cc/c89/c99 or aCC with -Ae.
                     The following is the list of default -D flags:
                     -AP:
                     -D__hpux -D__ia64=1 -D_BIG_ENDIAN=1 -D__STDCPP__
                     -D__HP_aCC=version-string

Thanks for the excellent resource!

MC