Handle compilation failures

[Notgnoshi]

These can happen for a number of reasons:

• Your compilation database might include a source file that's been deleted
• Your compilation database might be missing certain #defines
• #pragma once could be treated as an error

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• Add a --compile-fail flag that exits the includegraph.py script on compilation failure.
• Should nodes for failed TUs be styled?
• If the first error is in a header, should the whole path from the header to the TU be styled?
• If preprocessing fails, are any linemarkers parsed?

[opello]

Another example of a failure that we ran into was when the generated command included arguments not supported by the compiler (-m32 was one). It seems like supporting filtering out arbitrary arguments is a good feature from the command line?

Might be addressed by #9 depending on the implementation.