I'm afraid this didn't do anything really, but shift the error by one line :P

g++ -c -I/usr/include -I./include -I. -I/usr/local/include/taglib -DPERL_USE_SAFE_PUTENV -fno-strict-aliasing -pipe -I/usr/local/include -DUSEIMPORTLIB -O3 -DVERSION=\"1.43\" -DXS_VERSION=\"1.43\" "-I/usr/lib/perl5/5.8/cygwin/CORE" -DNO_DOXYGEN TagLib.c
In file included from TagLib.xs:16:
./include/iconv_wrap.h: In function `size_t iconv_wrap(void*, char**, size_t*, char**, size_t*)':
./include/iconv_wrap.h:31: error: invalid conversion from `char**' to `const char**'
./include/iconv_wrap.h:31: error: initializing argument 2 of `size_t libiconv(void*, const char**, size_t*, char**, size_t*)'
TagLib.c:1335:15: warning: extra tokens at end of #ifdef directive
TagLib.c:1336:15: warning: extra tokens at end of #undef directive
TagLib.c:1339:16: warning: extra tokens at end of #undef directive
TagLib.c:1344:1: warning: "do_open" redefined
TagLib.c:1343:1: warning: this is the location of the previous definition
TagLib.c:1346:1: warning: "do_close" redefined
TagLib.c:1345:1: warning: this is the location of the previous definition
make: *** [TagLib.o] Error 1