- More consistent with other system components.

- This will be used for TLS pages, among other things.

- Also add a missing include.

- helpful to disambiguate Kernel::Memory namespace.

- Adds memory alignment fixes.

kernel/thread: Resolve -Wswitch warnings

CMakeLists: Specify -Wextra on linux builds

buffer_cache: Return handles instead of pointer to handles

externals: Use shared libraries if possible

This is mostly done by pkgconfig.
I've focused on the larger and more stable libraries.