Generate GNU-style pkcs11.h at compile time

[ueno]

Currently we use C preprocessor macros to rename symbols/types/struct members in pkcs11.h to match the GNU coding style. These are a bit intrusive and prone to cause name conflicts.

Instead, it would be nice to generate a separate header, say pkcs11-gnu.h, from the header using non-GNU convention at compile time.

Then it could be included from pkcs11.h if the GNU convention is enabled.

[nmav]

That certainly makes sense especially if in the future, the pkcs11.h from the oasis group becomes open-source license friendly. That would allow p11-kit shipping the original header with extensions defined in additional headers (pkcs11x.h and pkcs11-gnu.h)