tests: Make yosys write $true/$false/$undef definitions.
tests: Make yosys write $true/$false/$undef definitions.

The lack of definitions was causing vpr to segfault.

From @kmurray on
https://github.com/verilog-to-routing/vtr-verilog-to-routing/issues/318

> The root cause is that $true is un-driven in your .eblif input, which
> causes it to be swept by VPR's netlist cleaning. This then means VPR
> can't identify the input (D pin) of the latch when writing the atom
> netlist.

Signed-off-by: Tim 'mithro' Ansell <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@mith.ro>

SymbiFlow/symbiflow-arch-defs,SymbiFlow/symbiflow-arch-defs