libcacard: add G_BEGIN/END_DECLS
libcacard: add G_BEGIN/END_DECLS

If the compiler in use is a C++ compiler, adds extern "C" around the
header.

Signed-off-by: Marc-André Lureau <a6f2b960a4aca61381fc650a67901b2ac8e83e6d@gmail.com>

SPICE/libcacard,SPICE/libcacard