2.3.2 does not find libiconv on macOS

Release 2.3.2 (or rather, the configure script), which was released
today, no longer recognizes libiconv, at least on the current version
of macOS (26.4.1).

| dennis@coredump:~% sw_vers
| ProductName:		macOS
| ProductVersion:		26.4.1
| BuildVersion:		25E253

2.3.1:

| dennis@coredump:~/src/mutt-2.3.1% ./configure && make
| [...]
| dennis@coredump:~/src/mutt-2.3.1% grep 'ICONV' config.h
| #define HAVE_ICONV 1
| #define HAVE_ICONV_H 1
| #define HAVE_ICONV_T_DEF 1
| #define ICONV_CONST
| #define ICONV_NONTRANS 0
| dennis@coredump:~/src/mutt-2.3.1% otool -L ./mutt
| ./mutt:
| 	/usr/lib/libncurses.5.4.dylib (compatibility version 5.4.0, current version 5.4.0)
| 	/usr/lib/libiconv.2.dylib (compatibility version 7.0.0, current version 7.0.0)
| 	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1356.0.0)
| dennis@coredump:~/src/mutt-2.3.1%

2.3.2:

| dennis@coredump:~/src/mutt-2.3.2% ./configure && make
| [...]
| dennis@coredump:~/src/mutt-2.3.2% grep 'ICONV' config.h
| /* #undef HAVE_ICONV */
| /* #undef HAVE_ICONV_H */
| /* #undef HAVE_ICONV_T_DEF */
| #define ICONV_CONST
| /* #undef ICONV_NONTRANS */
| dennis@coredump:~/src/mutt-2.3.2% otool -L ./mutt
| ./mutt:
| 	/usr/lib/libncurses.5.4.dylib (compatibility version 5.4.0, current version 5.4.0)
| 	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1356.0.0)
| dennis@coredump:~/src/mutt-2.3.2%

The m4/iconv.m4 file differs between the two versions, but I'm not
familiar enough with it to figure out what´s going wrong.

Dennis