check in configure script if iconv() needs CONST

configure.ac

@@ -157,6 +157,26 @@ if test x$enable_iconv = xyes; then
 	if test x$enable_iconv = xyes; then
 		AC_CHECK_LIB(iconv,main,MPD_LIBS="$MPD_LIBS $ICONV_LIBS",)
 		AC_DEFINE(HAVE_ICONV,1,[Define to use iconv])
+		AC_MSG_CHECKING([for iconv declaration])
+		AC_CACHE_VAL(proto_iconv, [
+			AC_TRY_COMPILE([
+#include <stdlib.h>
+#include <iconv.h>
+extern
+#ifdef __cplusplus
+"C"
+#endif
+#if defined(__STDC__) || defined(__cplusplus)
+size_t iconv (iconv_t cd, char * *inbuf, size_t *inbytesleft, char * *outbuf, size_t *outbytesleft);
+#else
+size_t iconv();
+#endif
+], [], iconv_arg1="", iconv_arg1="const")
+		        proto_iconv="extern size_t iconv (iconv_t cd, $am_cv_proto_iconv_arg1 char * *inbuf, size_t *inbytesleft, char * *outbuf, size_t *outbytesleft);"])
+			proto_iconv=`echo "[$]am_cv_proto_iconv" | tr -s ' ' | sed -e 's/( /(/'`
+			AC_MSG_RESULT([$]{ac_t:-}[$]proto_iconv)
+			AC_DEFINE_UNQUOTED(ICONV_CONST, $proto_iconv_arg1,
+				[Define as const if the declaration of iconv() needs const.])
 	fi
 	CFLAGS=$oldcflags
 	LIBS=$oldlibs

src/charConv.c

@@ -83,7 +83,7 @@ int setCharSetConversion(char * to, char * from) {
 	return -1;
 }
 
-char * convStrDup(char * string) {
+char * convStrDup(ICONV_CONST char * string) {
 	if(!char_conv_to) return NULL;
 
 	if(char_conv_same) return strdup(string);

src/charConv.h

@@ -23,7 +23,7 @@
 
 int setCharSetConversion(char * to, char * from);
 
-char * convStrDup(char * string);
+char * convStrDup(ICONV_CONST char * string);
 
 void closeCharSetConversion();