The variable pages never said what happens when the mode isn't set.
The find commands fall back to BOTH. The mode descriptions also only
talked about CMAKE_FIND_ROOT_PATH, but CMAKE_SYSROOT is re-rooted the
same way, and ONLY still searches under CMAKE_STAGING_PREFIX.
Fixes: #27298
Add support for PRIVATE header sets, analogous to the existing
INTERFACE header sets support. A key difference between the two is
the way they handle build and usage requirements. INTERFACE
header sets rely on the original target's INTERFACE, whereas PRIVATE
header sets copy across various properties from the original target.
Generated files need special handling for PRIVATE header sets.
Add a dependency on the original target to the verification target to
ensure such generated files will exist.
Fixes: #23448
Daksh Mamodiya