Merge "Revert "Remove external/libcxxabi in favor of prebuilt"" into main am: ab85fcc31a am: 76c5425fa5

Original change: https://android-review.googlesource.com/c/platform/external/libcxxabi/+/3061870

Change-Id: Ib420d2e483dd558deee2a856a0eedd3120a9f0c2
Signed-off-by: Automerger Merge Worker <[email protected]>