Restore use of __builtin_cheri_get_invoke_data_cap() in implementing
cheri_getidc() now that compiler bugs and compiler/hardware are back
in sync regarding the CHERI ISA.
Add string for user-defined capability exception.
Rename user-defined capability exception to user-defined permission
exception.
Add C wrappers for CCheckType and CCheckPerm.
Add baby test cases for CCheckPerm to /bin/cheritest.
Add definitions for user-defined permission bits; redefine current
permissions in a way that makes it easier to visually compare with
the CHERI Architecture Document.
Add a constant definition for user-defined permission exceptions.
Rename user-permission exception constant based on discussion.