[kernel] Revive the debugcon logger as a kernel thread

The debugcon logger is now separate from logger::output, and is instead
a kernel-internal thread that watches for logs and prints them to the
deubcon device.

assets/build/base.yaml

@@ -13,6 +13,8 @@ variables:
     "-fcolor-diagnostics",
     "-U__STDCPP_THREADS__",
     "-D_LIBCPP_HAS_NO_THREADS",
+    "-D__jsix_config=${build_config}",
+    "-D__jsix_config_${build_config}",
     "-DVERSION_MAJOR=${version_major}",
     "-DVERSION_MINOR=${version_minor}",
     "-DVERSION_PATCH=${version_patch}",