There are two things to investigate here:

1. How does GN track header files when building Hafnium, i.e. does a change in a header file trigger rebuild of all source files that include it?
2. We've seen the build system not recompile the Linux driver after a change to one of Hafnium's header files (inc/vmapi/hf/*).
   1. make needs to rebuild the driver if a header file changes
   2. GN needs to run make on the driver if a header file changes

(Migrated from b/141459219.)