[all] Remove dependencies on non-freestanding libc

This is the first of two rather big changes to clean up includes
throughout the project. In this commit, the implicit semi-dependency on
libc that bonnibel adds to every module is removed. Previously, I was
sloppy with includes of libc headers and include directory order. Now,
the freestanding headers from libc are split out into libc_free, and an
implicit real dependency is added onto this module, unless `no_libc` is
set to `True`. The full libc needs to be explicitly specified as a
dependency to be used.

Several things needed to change in order to do this:

- Many places use `memset` or `memcpy` that cannot depend on libc. The
  kernel has basic implementations of them itself for this reason. Now
  those functions are moved into the lower-level `j6/memutils.h`, and
  libc merely references them. Other modules are now free to reference
  those functions from libj6 instead.
- The kernel's `assert.h` was renamed kassert.h (matching its `kassert`
  function) so that the new `util/assert.h` can use `__has_include` to
  detect it and make sure the `assert` macro is usable in libutil code.
- Several implementation header files under `__libj6/` also moved under
  the new libc_free.
- A new `include_phase` property has been added to modules for Bonnibel,
  which can be "normal" (default) or "late" which uses `-idirafter`
  instead of `-I` for includes.
- Since `<utility>` and `<new>` are not freestanding, implementations of
  `remove_reference`, `forward`, `move`, and `swap` were added to the
  `util` namespace to replace those from `std`, and `util/new.h` was
  added to declare `operator new` and `operator delete`.

src/libraries/j6/channel.cpp

@@ -2,13 +2,12 @@
 // but should not include the user-specific code.
 #ifndef __j6kernel
 
-#include <string.h>
-
 #include <arch/memory.h>
 #include <j6/channel.hh>
 #include <j6/condition.hh>
 #include <j6/errors.h>
 #include <j6/flags.h>
+#include <j6/memutils.h>
 #include <j6/mutex.hh>
 #include <j6/syscalls.h>
 #include <j6/syslog.hh>