Fix nested redundant include for int128.h (#9)

Update to abseil-cpp source tag 20211102.0 (#8)

Merge pull request #6 from firebase/rw-xcode13-fixes

Fix invalid excludes surfaced in Xcode 13 beta 1

Delete testing header (#5)

Revert "Exclude doesn't seem to work for module headers"

This reverts commit ecbcece.

Merge pull request #2 from firebase/toolchain-fixes

Toolchain fixes

README update