MFC r277300 (by smh): Mechanically convert cddl sun #ifdef's to illumos

Since the upstream for cddl code is now illumos not sun, mechanically
convert all sun #ifdef's to illumos #ifdef's which have been used in all
newer code for some time.

Also do a manual pass to correct the use if #ifdef comments as per style(9)
as well as few uses of #if defined(__FreeBSD__) vs #ifndef illumos.

MFC r283025:
As dtrace(1) processes D libraries under /usr/lib/dtrace, the compiler may
return an error if one of the depends_on directives in a library is not
satisfied. In this case, libdtrace is supposed to ignore the library and
carry on. However, the remainder of the library may still be buffered by
the lexer, causing libdtrace to erroneously continue processing it on the
next call to yyparse(). Fix this by explicitly flushing the input buffer
each time the compiler state is reset.

MFC 267929, 267937, 267939, 267940, 267941, 267942, 267987, 268006:

2915 DTrace in a zone should see "cpu", "curpsinfo", et al
2916 DTrace in a zone should be able to access fds[]
2917 DTrace in a zone should have limited provider access
4477 DTrace should speak JSON
Add stubs for CTF functions which are not yet implemented.
4474 DTrace Userland CTF Support
4475 DTrace userland Keyword
4476 DTrace tests should be better citizens
4479 pid provider types
4480 dof emulation is missing checks
4471 DTrace count() with histogram
4472 DTrace full width distribution histograms
4473 DTrace frequency trails

MFC r283025:
As dtrace(1) processes D libraries under /usr/lib/dtrace, the compiler may
return an error if one of the depends_on directives in a library is not
satisfied. In this case, libdtrace is supposed to ignore the library and
carry on. However, the remainder of the library may still be buffered by
the lexer, causing libdtrace to erroneously continue processing it on the
next call to yyparse(). Fix this by explicitly flushing the input buffer
each time the compiler state is reset.

MFC 267929, 267937, 267939, 267940, 267941, 267942, 267987, 268006:

2915 DTrace in a zone should see "cpu", "curpsinfo", et al
2916 DTrace in a zone should be able to access fds[]
2917 DTrace in a zone should have limited provider access
4477 DTrace should speak JSON
Add stubs for CTF functions which are not yet implemented.
4474 DTrace Userland CTF Support
4475 DTrace userland Keyword
4476 DTrace tests should be better citizens
4479 pid provider types
4480 dof emulation is missing checks
4471 DTrace count() with histogram
4472 DTrace full width distribution histograms
4473 DTrace frequency trails