CI: rfl: build the generated doctests

We were already generating the doctests, which should already catch most issues with our hack around `--test-builder` and `--no-run`. However, we were not building the result of that transformation, thus build it for completeness and to ensure the hack may not have produced something completely broken. In the worst case, we can revert it. Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

src/ci/docker/scripts/rfl-build.sh

@@ -65,4 +65,5 @@ make -C linux LLVM=1 -j$(($(nproc) + 1)) \
 make -C linux LLVM=1 -j$(($(nproc) + 1)) \
  samples/rust/rust_minimal.o \
  samples/rust/rust_print.o \
- drivers/net/phy/ax88796b_rust.o
+ drivers/net/phy/ax88796b_rust.o \
+ rust/doctests_kernel_generated.o