While the (removed) comment is correct and the frontend can be called in
different modes, both `swift build` and `xcodebuild` always use
`-primary-files` when compiling Swift projects.
The other mode was present only within our test runner (`qltest.sh`), so
removing it and doing what the official build systems do simplifies our
code base.
Additionally, file archival is now a separate function/operation.
This checks in the trapgen script generating trap entries in C++.
The codegen suite has been slightly reorganized, moving the templates
directory up one level and chopping everything into smaller bazel
packages. Running tests is now done via
```
bazel run //swift/codegen/test
```
With respect to the PoC, the nested `codeql::trap` namespace has been
dropped in favour of a `Trap` prefix (or suffix in case of entries)
within the `codeql` namespace. Also, generated C++ code is not checked
in in git any more, and generated during build. Finally, labels get
printed in hex in the trap file.
`TrapLabel` is for the moment only default-constructible, so only one
single label is possible. `TrapArena`, that is responsible for creating
disjoint labels will come in a later commit.
