HP-UX 11i Version 1.5 Release Notes, September 2001

Programming
Machine Dependent Headers
Chapter 7114
Machine Dependent Headers
The machine dependent headers in the /usr/include/machine
directory have been restructured. Applications including the headers
from the /usr/include/machine directory will need to make minor
modifications to #include statements accordingly in order to compile.
NOTE Please note that source compatibility is not guaranteed for applications
which include any undocumented headers.