x/build: git history rewrite

[bradfitz]

I'm rewriting Go's history to remove a bad merge (66b2401) and its revert commit (184c706) while preserving the two valid commits that follow.

Steps:

git reset --hard 0e0cd70ecf6b5f0d9c8271f68b8fcc9f85cd6598
git cherry-pick 198679832ad627ee88ed5b3d75cc96819889a51c
git cherry-pick d592ac1c96efa323019a03133bea0ae7c6e0be32

/cc @andybons @ianlancetaylor @FiloSottile

[bradfitz]

Done.

And left comments on the two CLs which had their git commits rewritten:

https://go-review.googlesource.com/c/go/+/121915/3
https://go-review.googlesource.com/c/go/+/121916/4

[mvdan]

Thanks for taking care of this, @bradfitz!

[bradfitz]

For the record, I also ended up having to clean up some datastore entities in the build.golang.org App Engine app and then restart gitmirror.

We should root out all these issues in gitmirror + the x/build/app so force pushes aren't so painful in the future.