Tracking bug: enabling DFT-based fuzzing

[Dor1s]

There are three main components:

1. Build / test support in OSS-Fuzz: this is tracked in Proposal: DFT-based fuzzing oss-fuzz#1632

2. Job support on ClusterFuzz side: we don't need a new job for DFT-based fuzzing, but we do need a separate build. This creates a problem: how do I enable a build on OSS-Fuzz side (project.yaml is the obvious answer), but do not create any additional jobs on CF side?

3. Strategy support on ClusterFuzz: might get too complicated, given that we need to download a separate build for that.

[Dor1s]

While writing this, I came up to another solution:

1. Set up DataFlow build in a way that it would have both ASan and DFSan binaries in the same archive.

2. Create a new Job for DataFlow config. Use it as an ASan job, except two minor differences:
   A) always use collect_data_flow option
   B) always use fork mode (LF currently crashes when collect_data_flow is used without fork mode)

Besides cleaner set up and less confusing strategy logic, this will also guarantee that we're using exactly the same source code for both ASan and DFSan binaries. I don't know whether this is a blocker, but it's definitely not beneficial to have mismatch in the corresponding ASan and DFSan binaries.

I'm really favoring this approach now. Will think more and pitch it to you in the meeting today :)

[Dor1s]

Thanks team for the discussion today. Now I'm leaning towards a new strategy again. I'll take a closer look at the code and try to predict / draft the changes necessary for enabling that.

[Dor1s]

The new functionality is broken into three CLs:

1. Add support for dataflow builds to the OSS-Fuzz setup handler (#503). #580: Add support for dataflow builds to the OSS-Fuzz setup handler.

2. Add support for auxiliary builds and use it for dataflow builds (#503). #582: Add AuxiliaryBuild class for extra builds like dataflow.

3. Add dataflow tracing strategy and refactor strategy parsing code (#503). #583: Add dataflow tracing strategy to libFuzzer launcher.