Install dtrace.h and depedencies

[arichardson]

Summary

This makes the minimum amount of changes to allow inclusion of dtrace.h
without all the solaris compatibility headers. Installing dtrace.h allows
compiling consumers of libdtrace (e.g. https://github.com/tmetsch/python-dtrace)
without requiring a copy of the source tree.
For python-dtrace I worked around this in https://github.com/tmetsch/python-dtrace/commit/58019c9a12022203a9ffda286dd8b41f1a5ace42
but being able to build the library without installed sources would be
extremely useful.

Test Plan

basic test program compiles, not tried tinderbox yet.

[arichardson]

Needs some more changes to avoid -Werror,-Wtypedef-redefinition

[arichardson]

Fix amd64 buildworld+buildkernel