[php-src] Issue #22413: Test failures with musl libc

Issue: https://github.com/php/php-src/issues/22413
Author: orlitzky

### Description

Follow-up to https://github.com/php/php-src/issues/13696. Musl is partially tested on the CI, but the Alpine job installs gnu-libiconv-dev which hides the following errors. With the latest php-8.5.7 release:

```
=====================================================================
FAILED TEST SUMMARY
---------------------------------------------------------------------
Bug #48147 (iconv with //IGNORE cuts the string) [ext/iconv/tests/bug48147.phpt]
Bug #52211 (iconv() returns part of string on error) [ext/iconv/tests/bug52211.phpt]
Bug #76249 (stream filter convert.iconv leads to infinite loop on invalid sequence) [ext/iconv/tests/bug76249.phpt]
EUC-JP to ISO-2022-JP [ext/iconv/tests/eucjp2iso2022jp.phpt]
iconv_mime_encode() [ext/iconv/tests/iconv_mime_encode.phpt]
```

I have an old PR at https://github.com/php/php-src/pull/16840 whose details I've mostly forgotten. I can start by cherry-picking the easy parts of that.



### PHP Version

```plain
PHP 8.5.7
```

### Operating System

Gentoo linux