This is needed when mixing D and C code, as it's possible to end up
witha combination of linkers and compilres such that C produces pdb
files but D does not.
This allows the harness to apply the version correctly, putting it in the right
place, dropping the right amount of numbers, etc.
pdb taking a version allows it to be more easily copied from the
shared_lib type.
Actually, GDC supports shared libraries since version 6.2, but on Debian
there are still issues with that version due to the standard library not
being compiled with PIC.
Therefore, we make a very conservative assumption here and only enable
the tests for GDC >= 7.0