vtkonly: keep system cflags from pkgconf dependencies
This fixes pkgconf dropping include paths due to its "system"
considerations.
As done for paraview in b35536ca (paraview: tell pkgconf to keep
"system" paths, 2024-07-03), via !918 (merged).
This fixes pkgconf dropping include paths due to its "system"
considerations.
As done for paraview in b35536ca (paraview: tell pkgconf to keep
"system" paths, 2024-07-03), via !918 (merged).