PR go/81324
    sysinfo.c: ignore ptrace_peeksiginfo_args from <linux/ptrace.h>
    
    With some versions of glibc and GNU/Linux ptrace_pseeksiginfo_args is
    defined in both <sys/ptrace.h> and <linux/ptrace.h>. We don't actually
    care about the struct, so use a #define to avoid a redefinition error.
    
    This fixes https://gcc.gnu.org/PR81324.
    
    Reviewed-on: https://go-review.googlesource.com/49290

From-SVN: r250324