`extern "C"` did not actually have an effect here since it only impacts
name mangling of functions, not structs (or other class types). Now this
can get in the way when we add functions to structs, e.g. templates are
not allowed in code with C-linkage.
Most of these were added in ad4b7741db, even though it was known that
this doesn't have any impact. Reason was because developers thought they
would have to add that to all direct and indirect includes to be able to
use a header in C++ (a common misconception). Now with most files
compiled in C++, it's obvious that this isn't the case.
Julian Eisel