check in configure script if iconv() needs CONST

git-svn-id: https://svn.musicpd.org/mpd/trunk@1523 09075e82-0dd4-0310-85a5-a0d7c8717e4f

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();