Fix date_strget DLL export

https://github.com/Hamlib/Hamlib/issues/882

src/misc.h

@@ -114,7 +114,7 @@ extern HAMLIB_EXPORT(int) parse_hoststr(char *hoststr, char host[256], char port
 
 extern HAMLIB_EXPORT(uint32_t) CRC32_function(uint8_t *buf, uint32_t len);
 
-extern char *date_strget(char *buf, int buflen, int localtime);
+extern HAMLIB_EXPORT(char *)date_strget(char *buf, int buflen, int localtime);
 
 #ifdef PRId64
 /** \brief printf(3) format to be used for long long (64bits) type */