Add all patches from base llvm/clang/lld/lldb 7.0 to devel/llvm70

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Summary

This adds all the patches that were applied in the past to the
clang700-import branch, under contrib/llvm. After these, there only
minimal diffs left between the port sources and the base sources.

Most of these remaining diffs are due to #ifdef shortcuts in the base
sources, because we don't compile certain features in. Other diffs are
because the port has applied a few changes that we don't have in base.

The list of PRs that were affected by the added patches is:

PR: 212343, 230604

I will also put this in the eventual commit message.

Test Plan

ideally this should be taken for an exp-run.