Enable getuid and getgid related syscalls on X86_SE

Enable getuid and getgid related syscalls on X86_SE

I've tested these on x86 and they work as expected.

In theory for 32-bit x86 we should have some sort of special
handling for the legacy 16-bit uid/gid syscalls, but in practice
modern toolchains don't use the 16-bit versions, and m5 sets the uid
and gid values to be less than 16-bits anyway.

This fix is needed for the perl spec2k benchmarks to run.