- 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.

Neither core nor web_services use OpenSSL nor LibreSSL.
However they need to link them as it's a requirement of httplib.
So let's declare this within httplib instead of core and web_services.

service: time: Implement CalculateStandardUserSystemClockDifferenceByUser.

The original idea of returning pointers is that handles can be moved.
The problem is that the implementation didn't take that in mind and made
everything harder to work with. This commit drops pointer to handles and
returns the handles themselves. While it is still true that handles can
be invalidated, this way we get an old handle instead of a dangling
pointer.

This problem can be solved in the future with sparse buffers.