[roll] Roll llvm-project/libc Revert "[libc] Add realpath to linux entrypoints" (#215156)

Reverts llvm/llvm-project#212925, the tests assume that `/tmp` is a
real, valid directory on the system, which is not true for all
buildbots. `libc-riscv32-qemu-yocto-fullbuild-dbg` in particular seems
to have a symlink or similar from `/tmp` to `/var/volatile/tmp`. See
https://github.com/llvm/llvm-project/pull/212925#issuecomment-5234167255.

GitOrigin-RevId: efe96c53557041be11e7fb4d43e6448cc09f6062
Original-Revision: 12032e5927915fd08574dd603505cb1c9c402db2

Rolled-Repo: https://llvm.googlesource.com/llvm-project/libc
Rolled-Commits: 35043b8c128b51..12032e5927915f
Roller-URL: https://cr-buildbucket.appspot.com/build/8673894172081761873
CQ-Do-Not-Cancel-Tryjobs: true
Cq-Include-Trybots: luci.turquoise.global.try:run-postsubmit-tryjobs
Change-Id: Icf70ee99779a48692981f932cd602e5e954baed2
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1751089
Commit-Queue: global-integration-roller@fuchsia-infra.iam.gserviceaccount.com <global-integration-roller@fuchsia-infra.iam.gserviceaccount.com>