I've committed the attached.  It tries to get the structs.exp test out 
of a hole that that the amd64 GDB appears to be digging for it:

> (gdb) PASS: gdb.base/structs.exp: ptype foo1; structs-tc
> p/c fun1()
> /home/cygnus/cagney/GDB/src/gdb/x86-64-tdep.c:438: internal-error: classify_argument: unknown argument type
> A problem internal to GDB has been detected,
> further debugging may prove unreliable.
> Quit this debugging session? (y or n) FAIL: gdb.base/structs.exp: p/c fun<n>(); call 1 structs-tc (GDB internal error)
> n
> /home/cygnus/cagney/GDB/src/gdb/x86-64-tdep.c:438: internal-error: classify_argument: unknown argument type
> A problem internal to GDB has been detected,
> further debugging may prove unreliable.
> Create a core file of GDB? (y or n) n

Andrew