The bazel -> cmake generator is currently not capable of handling
separate included generated cmake files making use of common C/C++
dependencies.
To work around this limitation, a single generated cmake is now in
place. Long-term, we should either:
* make the cmake generator handle common dependencies gracefully, or
* make the cmake generation aspect travel up `pkg_` rules `srcs`
attributes
so to avoid having to list the targets to be generated in the top-level
`BUILD` file.
Other things fixed:
* removed some warning spam about redefined `BAZEL_CURRENT_REPOSITORY`
* fixed the final link step, that was failing because `libswiftCore.so`
was not being linked.
A cmake generator in bazel is introduced allowing to import the Swift
extractor as a CMake project while keeping Bazel files as the source of
truth for the build.
Using the CMake project:
* requires bazel and clang to be installed and available on the command
line
* does not require a previous bazel build, however
* will require a CMake reconfiguration for changes to generated code
(like changes to the schema)
