clang: Upgrade to 18.1.8

[kraj]

Brings

• 3b5b5c1ec4a3 [libcxx] Align __recommend() + 1 by __endian_factor (#90292)
• 72c9425a79fd [libc++][NFC] Rewrite function call on two lines for clarity (#79141)
• 443e23eed24d Bump version to 18.1.8 (#95458)

Release announcement [1] [1] https://discourse.llvm.org/t/18-1-8-released/79725/1

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