[llvm-branch-commits] [libcxx] release/23.x: [libc++] Fix ungetc failing after xsgetn (#210951) (PR #212510)

[Louis Dionne via llvm-branch-commits]

ldionne wrote:

@philnik777 Are we missing another cherry-pick? https://github.com/llvm/llvm-project/actions/runs/30369155433/job/90326016892?pr=212510#step:4:4403

https://github.com/llvm/llvm-project/pull/212510