Thank you for your answers. I have really managed to improve the linking speed:
First I have tried to use the GOLD linker. Because I am using ubuntu, the package was available in the sources. But now, because I do not know the binutils and I could not find a useful documentation I do not know if I am using it now or not. I guess yes, because ld-- version gives "GNU gold (GNU Binutils for Ubuntu 2.20) 1.9" Nevertheless it did not help to reduce linking time. You have mentioned the -of command flag. For dmd there is no documentation about it in the help so I could not make it work. However during my try and error to use it I figured out that my guess how dmd links was not correct. It seems, that if the -c option is used (no linking) then for each .d file an .o file is created. However if the -c flag is not giving, only one .o file is created. I got to recognize that the output speed (-v flag) became extremely slow when -c was not used I wondered how this can be, because linking was not supposed to be done at that particular time anyway. After I have managed to separate compiling and linking (calling dmd with -c and then calling gcc with all object files and libraries) I could see that linking 250 Object files took 1 second! (Compared to 20 min if dmd does the job). So my guess is, that creating the one object file (not using -c) during compiling is very inefficient - and in consequence I have unfairly blamed the the linker for it. Torsten