[cdac-build-tool] Take baseline as a command line argument

[lambdageek]

Follow-up work item for #100650. In the above PR we made cdac-build-tool take a CDAC_BASELINE("name") preprocessor macro to encode the baseline into the data blob in the object file that we scrape.

There's no need to do that, and it also introduces complications in future scenarios when there's multiple object files (produced by a C/C++ compiler and the NativeAOT compiler, for example): we now need all of them to agree about the baseline.

Instead we should take the baseline name as an optional command line argument and update CMakeLists.txt to pass in an appropriate (possibly platform-specific) one.

This is relatively low-priority because the initial workflow is using an empty baseline.

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