C++: Fix IR generation for builtins and add flow through __builtin_bit_cast

[MathiasVP]

This PR does two things with the end goal of getting flow through this example:

void test() {
  unsigned long x = source();
  double d = __builtin_bit_cast(double, x);
  sink(d);
}

• First, we fix IR generation for builtins. We were not skipping children we could not translate, which caused the IR generation to fail since the first argument of __builtin_bit_cast is a TypeName which has no IR representation. This meant that __builtin_bit_cast had no operands in the IR (see the first commit which adds a test for this).

  We could have added IR generation for TypeNames, but that would involve introducing another IR instruction which I didn't really feel like doing since we currently have no use-cases for doing anything with TypeNames in any queries.

• Second, we add flow through __builtin_bit_cast by treating it as a conversion in dataflow.

Commit-by-commit review recommended

[jketema]

LGTM, but could we do a DCA run with uninterpreted queries enabled to see the impact this has on existing inconsistencies?

[MathiasVP]

LGTM, but could we do a DCA run with uninterpreted queries enabled to see the impact this has on existing inconsistencies?

I think I did? Although, it looked like these changes had 0 impact on the existing inconsistencies 😢

[jketema]

Do'h. I'm expecting to always see changes in that table, but that's with non-cached databases. Apologies.