target-alpha: implement getxuid and getxgid syscalls

target-alpha: implement getxuid and getxgid syscalls

This patch implemented the setxuid and setxgid syscalls for Alpha.
These syscalls return two values, both uid/euid and gid/egid.
In addition to returning the first value in $v0, the additional
value is returned in the $a4 register.

The syscalls are used instead of the separate syscalls for those values
used on other architectures (this is probably because Alpha Linux started
out syscall compatible with DEC/OSF/Tru64).

With this patch, the perlbmk benchmarks from Spec2000 run properly.

(Vince Weaver)

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5722 c046a42c-6fe2-441c-8c8c-71466251a162