Switch to libc++ prebuilt

Apex-Size-Increase: 1468 KiB for com.google.android.art.apex
Previous-Platform-Support: yes, the prebuilts work on API 30 and up
Aosp-First: AOSP-first (but really github.com/llvm/llvm-project)
Test-Info: upstream lit-based test suite, run automatically in upstream
  CI and manually with local Android devices

Test: m
Bug: 332594828
Change-Id: I5bc4ed71318e9459b2ed46e1f01d16a7dd49cf7f