[Groff] Make balks on preconv (OS X)

[Robert Goulding]

Just tried to make the latest snapshot, on Mac OS X.3.9.  The make 
fails with:

g++2 -I. -I. -I/Users/rgouldin/Data/groff-current/src/include 
-I/Users/rgouldin/Data/groff-current/src/include -DHAVE_CONFIG_H -g -O2 
 -c  preconv.cpp
preconv.cpp: In function `void conversion_iconv(FILE *, const string &, 
char *)':
preconv.cpp:669: passing `char **' as argument 2 of `libiconv(void *, 
const char **, size_t *, char **, size_t *)' adds cv-quals without 
intervening `const'
preconv.cpp:700: passing `char **' as argument 2 of `libiconv(void *, 
const char **, size_t *, char **, size_t *)' adds cv-quals without 
intervening `const'
make[2]: *** [preconv.o] Error 1
make[1]: *** [src/preproc/preconv] Error 2
make: *** [all] Error 2

Robert.