Add a memmove_c.
Add memcpy_c, memmove_c, and memset_c.
Use standard versions of headers.
Stub out timer support.  Syscall code doesn't build in sandbox mode and
I don't think it's worth trying to fix at this time.
Remove some duplicate softfloat bits provided by compiler-rt.
Stub out syscalls for now.  This breaks the cheripoint demo, but it
hasn't worked for quite some time anyway.