[roll] Roll llvm-project/libc be537e7..a84a84f (2 commits)

a84a84f:https://llvm.googlesource.com/llvm-project/libc/+/a84a84f5bb0149efe96ee88e07160399daba9837 [libc][math] Fix FP add/sub for signed-zero operands (#183243)
df4adb9:https://llvm.googlesource.com/llvm-project/libc/+/df4adb93d34fd393a62d0479a7db7d52bb84726f [libc][math] Optimize `asinpif` and `acospif` using estrin's scheme (#184286)

Rolled-Repo: https://llvm.googlesource.com/llvm-project/libc
Rolled-Commits: be537e74dcdd2a..a84a84f5bb0149
Roller-URL: https://cr-buildbucket.appspot.com/build/8688023243827792241
CQ-Do-Not-Cancel-Tryjobs: true
Cq-Include-Trybots: luci.turquoise.global.try:run-postsubmit-tryjobs
Change-Id: I4c4845d97eca938f54a8a827f539d6f4f5a993dc
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1529987
Commit-Queue: GI Roller <global-integration-roller@fuchsia-infra.iam.gserviceaccount.com>