Use clang-format-12 in presubmits (#9473)
Use clang-format-12 in presubmits (#9473)

We have to have some pinned version and there isn't really a strong
reason it has to be the same as our oldest supported version of clang.
Most devs have more recent clang versions, so the later version is
likely to be closer to what people have locally. clang-format-12 is
the newest version installed by default on the GitHub managed runners,
so it also saves us some apt nonsense.

Fixes https://github.com/google/iree/9154
google/iree,iree-org/iree,google/iree,iree-org/iree,google/iree,google/iree,google/iree,google/iree,iree-org/iree,google/iree,iree-org/iree,iree-org/iree,iree-org/iree,iree-org/iree