all: remove theory import path references

In Isabelle2020, when isabelle jedit is started without a session
context, e.g. `isabelle jedit -l ASpec`, theory imports with path
references cause the isabelle process to hang.

Since sessions now declare directories, Isabelle can find those files
without path reference and we therefore remove all such path references
from import statements. With this, `jedit` and `build` should work with
and without explicit session context as before.

Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>

licenses: convert license tags to SPDX

asmrefine: Add support for 64-bit architectures.

asmrefine: arch-split for machine word size.

Arch-split memory operations used when translating graph-lang.

asmrefine: update to Isabelle2019; reduce warnings

globally use session-qualified imports; add Lib session

Session-qualified imports will be required for Isabelle2018 and help clarify
the structure of sessions in the build tree.

This commit mainly adds a new set of sessions for lib/, including a Lib
session that includes most theories in lib/ and a few separate sessions for
parts that have dependencies beyond CParser or are separate AFP sessions.
The group "lib" collects all lib/ sessions.

As a consequence, other theories should use lib/ theories by session name,
not by path, which in turns means spec and proof sessions should also refer
to each other by session name, not path, to avoid duplicate theory errors in
theory merges later.

asmrefine: revert simplification of ghost_assertions

The previous simplfication broke SimplExportAndRefine.

Support extra specs, ctzl, clzl in SimplExport.

This patch permits the user to supply additional specs for functions
whose bodies were not imported (DONT_TRANSLATE or not present in parsed
C source). Those specs are exported by SimplExport.

The existing apparatus can import builtin functions like ctzl/clzl in C
sources by admitting them without bodies (DONT_TRANSLATE) and giving
them axiomatic Hoare triples (FNSPEC).

Translation validation then requires export of useful semantics. The user
can supply a made-up body, and show that it is a refinement of the body
that the parser created (derived from the FNSPEC and MODIFIES clauses).
The body must export out the graph language correctly. For ctzl/clzl etc
this is easy.

x64: create arch-specific CKernel

Repair SimplExport/GraphRefine.

WIP on WCET annotations.

Restore global valid assertions in graph refine.

The global-object pointer validity assertion is now created at
export time, and the graph refine mechanism now proves them. It
seems they were forgotten about once again in adjusting the globals
logic.

SEL4GraphRefine now completed.

These final changes complete the SEL4GraphRefine process. Some
cleanup remains to be done, especially in SEL4GlobalsSwap, but the
process is now mature and working, and the testing code
in SEL4GraphRefine can be discarded.

Success depends on seL4 commit 97d6bc96d54f1f0beafb25033b03b57ba54a5113
which is compatible with crefine and will be included in the repo
manifest immediately.

Import release snapshot.