Hi Soner,
thanks for your input. I found out that it was no problem to compile the demo game by Handoko, which is included in the latest allegro.pas. So the problem had to be in the makefile and voilà, in the file there are the following lines:
# Optimized compilation
# FLAGS = $(OPTOPT) $(PFLAGS) $(EFLAGS)
# Use next line instead to activate debug.
FLAGS = $(DBGOPT) $(PFLAGS) $(EFLAGS)
which I changed to
# Optimized compilation
FLAGS = $(OPTOPT) $(PFLAGS) $(EFLAGS)
# Use next line instead to activate debug.
# FLAGS = $(DBGOPT) $(PFLAGS) $(EFLAGS)
and now all the examples compile fine. Neither on Ubuntu nor on Fedora there are *-debug versions of allegro5, just the -dev packages.