Segher Boessenkool writes:

It is not.  -mcpu=powerpc64 doesn't select an ABI, and your
GCC presumably defaults to the 32-bit ABI.  Use -m64 on the
GCC command line, too, you need it, and it solves this issue
as a side effect.

No, actually the command line had -m64 on it.  The situation is this:

gcc -m64 -mtune=power4 works
gcc -m64 -mcpu=powerpc64 -mtune=power4 fails.

The problem is in the spec file where it works out what parameters to
pass to `as'.  Without any -mcpu it correctly defaults to passing
-mppc64 (when -m64 is given).  It then also has a list of -mcpu values
and the corresponding flag to pass to as, but powerpc64 isn't in that
list.  Thus with -mcpu=powerpc64 we don't get -mppc64 passed to as.

Paul.