[YOSYS][issue/3594] print stack of script commands upon error

[arcturusannamalai]

[YOSYS][issue/3594] print stack of script commands upon error; this is not a backtrace of program stack but of the Yosys script.
e.g.

-- Executing script file `./demo.ys' --

1. Executing Verilog-2005 frontend: ../yosys/f2.v
Parsing Verilog input from `../yosys/f2.v' to AST representation.
Successfully finished Verilog frontend.

2. Executing Verilog-2005 frontend: ../yosys/hello.v
Parsing Verilog input from `../yosys/hello.v' to AST representation.
Successfully finished Verilog frontend.

3. Executing CXXRTL backend.

3.1. Executing HIERARCHY pass (managing design hierarchy).

3.1.1. Finding top of design hierarchy..

3.2. Executing FLATTEN pass (flatten design).

3.3. Executing PROC pass (convert processes to netlists).

3.3.1. Executing PROC_CLEAN pass (remove empty switches from decision trees).
Cleaned up 0 empty switches.

3.3.2. Executing PROC_RMDEAD pass (remove dead branches from decision trees).
Removed a total of 0 dead cases.

3.3.3. Executing PROC_PRUNE pass (remove redundant assignments in processes).
Removed 0 redundant assignments.
Promoted 0 assignments to connections.

3.3.4. Executing PROC_INIT pass (extract init attributes).

3.3.5. Executing PROC_ARST pass (detect async resets in processes).

3.3.6. Executing PROC_ROM pass (convert switches to ROMs).
Converted 0 switches.

3.3.7. Executing PROC_MUX pass (convert decision trees to multiplexers).

3.3.8. Executing PROC_DLATCH pass (convert process syncs to latches).

3.3.9. Executing PROC_DFF pass (convert process syncs to FFs).

3.3.10. Executing PROC_MEMWR pass (convert process memory writes to cells).

3.3.11. Executing PROC_CLEAN pass (remove empty switches from decision trees).
Cleaned up 0 empty switches.

3.3.12. Executing OPT_EXPR pass (perform const folding).

ERROR: No such command: writx (type 'help' for a command overview)
Error while executing script:
	Running script on file './demo.ys'
---------------------------------
   1 read_verilog ../yosys/*.v
   2 write_cxxrtl demo.cxx
-->3 writx
---------------------------------

[arcturusannamalai]

Fork off from branch #3757 as per maintainer request