Convert both files simultanously, because the SI_UNITS define works
either under C or under C++.
This was painful, because initialization of struct-members has to
be done in order of definition in C++. And it was completely out
of order. However, as long as not all is C++, we can't use
default initialization directly in the struct definition. :(
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>