Checkpoint work in progress on memory safety.
Checkpoint more changes
Checkpoint a completed pushdown of __capability.
Don't try to build files that crash the backend.

This results in a failing build, but let me finish pushing down
__capability.
more cleanups
Fix some variable shadowing.
Checkpoint work in progress on memory safety.
add missing file from 7bd4052
Fix a bunch of cases of passing __capablity u_char * to printf's %s.
Remove a hack that let this compile with an earlier clang.
Use tcpdump macro names for some string functions.
Add memcpy_c* to libcheri.

This ideally belongs in libc.
Disable some decryption code when using capabilities.

This code violates the constness of packet processing in horriable ways.
Some signficant rearchitecture work is required to fix it so just
disable it for now as it's optional.
More pushing down of memory safety.

tcpdump, cheri_tcpdump, and tcpdump-helper all build now.
Improve the quality of no-op definitions.
Define pcap_datalink_val_to_name.

Remove a bunch of stuff that was or should have been #if 0'd before.
Remove an unneeded decleration that shadowed another.
Add strnlen_c() and strncpy_c*().
Fix more cases of printing strings from packets.

Refactor the way we do this in most causes with p_strdup and p_strfree
macros.  In the non-capablity case they are simply the pointer (with a
cast to shut up the const check) and a no-op do-while block.
Enable -Werror and ignore some harmless string format warnings.