CVE-2025-26519: musl libc: input-controlled out-of-bounds write primitive in iconv()

[leahneukirchen]

wasi-libc vendors parts of musl-libc and is thus suspectible to the same iconv bug found in musl since 0.9.13, for details and patches see: https://www.openwall.com/lists/oss-security/2025/02/13/2

[abrown]

@sunfishcode plans to apply the two upstream patches fixing this to #557.