Add LLVMPassManagerBuilderRef Extensions

[talyian]

Add some missing methods on LLVMPassManagerBuilderRef

[msftclas]

All CLA requirements met.

[EgorBo]

btw, does LlvmSharp support the new Pass manager?

[tannergooding]

LLVMSharp just wraps all the APIs publicly exposed by the underlying LLVM 8.0.0 header files.

AFAIK, all the bindings are declared correctly so they should work if they are exposed.

[tannergooding]

nit: This repo uses allman style braces (new line before the brace) as per the .editorconfig file:
https://github.com/microsoft/LLVMSharp/blob/master/.editorconfig#L254

If you are using an IDE or editor with a compatible .editorconfig extension and a supported Roslyn plugin (VS has one built-in and VS Code has one you can install), then the document should be automatically formatted with the correct rules as you are working.

[tannergooding]

Overall LGTM.

Just a nit where the coding style deviates from the .editorconfig.

[tannergooding]

Thanks!