But this only works as you build gdc and gcc separately. I.e. for gdc,
you build gcc+gdc, then throw away everything but gdc related
executables. Then you compile gcc with different --with-pkgversion for
the gcc package.

However, this has the problem that your gcc executable now does not
properly forward .d files to gdc as that build did not have --enable-
languages=d. The supported way to do this is build all gcc based
compilers at once. But then you can't use --with-pkgversion as it will
apply to all compilers.

--
Johannes