fix iconv use on mingw

include/libtorrent/config.hpp

@@ -167,6 +167,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #define TORRENT_USE_ICONV 0
 #define TORRENT_USE_LOCALE 1
 #endif
+#define TORRENT_ICONV_ARG (const char**)
 #define TORRENT_USE_RLIMIT 0
 #define TORRENT_USE_NETLINK 0
 #define TORRENT_USE_GETADAPTERSADDRESSES 1
@@ -276,6 +277,10 @@ inline int snprintf(char* buf, int len, char const* fmt, ...)
 #define TORRENT_UPNP_LOGGING
 #endif
 
+#ifndef TORRENT_ICONV_ARG
+#define TORRENT_ICONV_ARG (char**)
+#endif
+
 // libiconv presence, not implemented yet
 #ifndef TORRENT_USE_ICONV
 #define TORRENT_USE_ICONV 1

src/escape_string.cpp

@@ -621,8 +621,10 @@ namespace libtorrent
 		ret.resize(outsize);
 		char const* in = s.c_str();
 		char* out = &ret[0];
-		// posix has a weird iconv signature
-		size_t retval = iconv(h, (char**)&in, &insize,
+		// posix has a weird iconv signature. implementations
+		// differ on what this signature should be, so we use
+		// a macro to let config.hpp determine it
+		size_t retval = iconv(h, TORRENT_ICONV_ARG &in, &insize,
 			&out, &outsize);
 		if (retval == (size_t)-1) return s;
 		// if this string has an invalid utf-8 sequence in it, don't touch it