Dtrace support

[mattmacy]

Code exists but is broken on POWER9.

[gromero]

@mattmacy Hi! Do you have a reproducer for this issue. At least dtrace -n 'dtrace:::BEGIN { printf("Hello FreeBSD!\n"); }' works for me on a P9 VM. Thank you.

[chmeeedalf]

How is DTrace broken? I've run plenty of traces and they work fine. The only thing I'm aware of is the CTF data is broken, due to overflow in the type table, and many duplicate type entries. The tracing itself works.