I have ever found MSVC building is failing , but now it's working fine, I want to know why

The buildbot ever showed that cmake generating the msvc sln file
failure, but few days later, it's fixed.
How it's fixed, I doesn't see the information.
Is it downgrade the msvc or other solutions?

You can subscribe to llvm-commit and clang-commit to receive an email
on every commit made by developers.
Or you can run 'svn log file' to see change log of a file.