Constification to appease the C++ gods:

fidodefs.h:47:27: warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
 #define FIDO_CHARSET_UTF8 "CHRS: UTF-8 4" /* FTS-5003 */
                           ^
writemsg.cpp:645:15: note: in expansion of macro 'FIDO_CHARSET_UTF8'
    *charset = FIDO_CHARSET_UTF8;