gdbserver build broken on amd64-linux

[Joel Brobecker]

> How about ths instead?
> 
> #ifndef ARCH_GET_FS
> #define ARCH_SET_GS 0x1001
> #define ARCH_SET_FS 0x1002
> #define ARCH_GET_FS 0x1003
> #define ARCH_GET_GS 0x1004
> #endif

Yes, that should work too. I'm curious as to why these macros are not
defined for me, or said differently how it is that they are defined for
others (assuming others can build this code on amd64-linux unmodified).

-- 
Joel