What is Int64_t? Used in libstdc++v3/libmath/signbitl.c

[Greg Freemyer]

Background:
    GCC:        A recent snapshot.
    Computer: Dec AlphaServer      (several years old)
    OS:          Tru64 V5.1               (i.e. The latest release. 
                                                   Previously known as Digital UNIX, or Ultrix before that.)

I downloaded and compiled the latest gcc snapshot a couple of days ago.

After the bootstrap compilation process was done I got an error:
    Int64_t is undefined.

I have grep'ed the entire source code and the only reference to this
token is in libstdc++v3/libmath/signbitl.c

Could someone tell me where Int64_t is supposed to be typecast and what
the typecast is supposed to be.

Thanks
Greg Freemyer
The Norcross Group