libstd: use libpanic_abort instead of libpanic_unwind am: ba4a587506

Original change: https://android-review.googlesource.com/c/platform/prebuilts/rust/+/1560037

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I20793d0aa2a91f945b46cbfe93e75e334e46690e
tree: 3a771fa7e175efa3b625380c2440b7cde92c6033
  1. bootstrap/
  2. darwin-x86/
  3. linux-x86/
  4. tests/
  5. Android.bp
  6. OWNERS