How to get the VHDL linter to work ?

## Information

**VIM version**

Operating System: Windows 10

## What went wrong

I'm trying out this plugin for the first time. I managed to get the linter for python to work, but I haven't been lucky with VHDL. I have model sim installed, which means vcom is available from the command line. I also tried it with ghdl, but didn't have any success there either.

## Reproducing the bug

Here's my current vimrc setup. As I mentioned, linting works on python.

```
let g:ale_set_signs = 0

let g:ale_lint_on_text_changed = 'never'
let g:ale_lint_on_insert_leave = 0
let g:ale_lint_on_enter = 0
let g:ale_lint_on_filetype_changed = 0
let g:ale_lint_delay = 0

let g:ale_echo_msg_error_str = 'E'
let g:ale_echo_msg_warning_str = 'W'
let g:ale_echo_msg_format = '[%linter%] [%severity%] %s'

let g:ale_statusline_format = ['Errors: %d', 'Warnings: %d', '']

"let g:ale_vhdl_ghdl_executable = 'D:\PortableApps\Neovim\plugins\ale\linters\ghdl\bin\ghdl.exe'

let g:ale_vhdl_vcom_executable = 'vcom'
let g:ale_vhdl_vcom_options = '-2008 -quiet -lint'

let g:ale_linters = {
\ 'vhdl': ['vcom'],
\ 'python': ['pylint'],
\}
```

No repository file or test is named. Start with the supplied vimrc and reproduce the VHDL setup on Windows using the configured vcom and tried ghdl executables; done means the ALE VHDL linter reports diagnostics, or the missing configuration or failure is documented.

Written by the indexing model from the issue text.