listfuncs subcommand for dbx: Display the list of functions

Format

listfuncs [filename]

The listfuncs subcommand displays a list of functions associated with each file in the program.

If the listfuncs subcommand is used without arguments, the function for every file in the program will be listed.

The listfuncs subcommand can be run only while the dbx debug program is running.

To list all functions in all files, enter:
```
listfuncs
```
To list the function only for file mypgm.c, enter:
```
listfuncs mypgm.c
```

The func subcommand.