MFC r249426;

MFC	r249426;

Merge change from illumos:

3519 DTrace fails to resolve const types from fbt
3520 dtrace internal error -- token type 316 is not a valid D
     compilation token
3521 clean up dtrace unit tests

Illumos Revision:	e98f46c

Reference:
https://www.illumos.org/issues/3519
https://www.illumos.org/issues/3520
https://www.illumos.org/issues/3521

Tested by:	Fabian Keil
Obtained from:	Illumos

git-svn-id: svn://svn.freebsd.org/base/stable/9@256004 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f