I mistyped.  The X11R6.3 code uses "__alpha" or "__alpha__",
both of which are predefined in NetBSD.

I also see tests for "ultrix" and "__osf__".
Anyone know what Digital Unix predefines?

I also see "linux" and "__alpha__" together,
indicating that it may run on linux/alpha.

Xnest complains:

Getting interface configuration: Device not configured

This is from the ioctl SIOCGIFCONF in access.c, with fd==1.

The window does come up, and is painted with the root weave pattern.

Attempting to bring up an xterm yields:

X Error of failed request:  BadValue (integer parameter out of range for operation)
  Major opcode of failed request:  1 (X_CreateWindow)
  Value in failed request:  0x21
  Serial number of failed request:  23
  Current serial number in output stream:  31

The nested root window flashes white momentarily while
the xterm tries to start up, then returns to root weave.

-Dave