Always return a status value.
cheri_fd_write_c() should take a const capability to write out.
Passify the compile by casting away const from an argument to
cheri_ptr().
Reenable -Werror.

The libc files in cheritest-helper have moved to libc_cheri.
Silence a warning by explictily casting away a const.
Eliminate the need for a read() syscall stub when using decode_png
in readpng-cheri-helper.
We can use the installed png headers.
Cast away the volatile qualifier when passing a pointer to
memcpy_tocap().
Add cerror.S to support direct syscalls using the standard generated .S
files.
Rely more on libc_cheri for common functions.
Don't close the fd when we aren't using one.
Directly query the mips cycle counter rather than making a sysarch call.
This doesn't actually build on amd64 at this point so remove stray
support.

This could be fixed, but doesn't seem worth the trouble at this time.
Build with -Werror to catch things like subtraction from capabilities.
Avoid subtraction from a capability by regenerating the expected result
from the original, unincremented one.
Avoid pointer subtraction by only incrementing if it makes sense.

Add a comment that this function has side effects in the capability
version.
Avoid the need to decrement a pointer by avoiding unnecessicary
increments.
Avoid the need to decrement a pointer by avoiding unnecessicary
increments.
Declare cheri_system_clock_gettime() and call it correctly.
Convert pngbox.c to use CHERI-Clang and the C invoke routine.