Recent LLVM builds fail at the CI

[ddobrev]

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The reason is that Directory.Build.props is somehow improperly invoked and creates a mislocated config.props the invocation of which in turn breaks the build.

[tritao]

Can we close this now?

[ddobrev]

I'm afraid not. I am forced to keep a branch with this file added for updating LLVM because otherwise its builds fail. The new build system relies on generating the projects of CppSharp in order to create config.props. However, to build LLVM we don't need CppSharp. We need to rewrite the scripts in such a manner that building CppSharp or LLVM is completely independent.