Motivation / Problem

User on IRC reported problems compiling on Linux where the allegro driver was failing. Turns out, v5 was installed, where we only work with v4.

Description

On some distros allegro v5 is called allegro-5, but on some others
it is not. So this should fix for all distros that allegro v5 is
not being picked up, and only v4 is.

Limitations

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker