Always hash files when building from release tarball

Always hash files when building from release tarball

The CMake logic to check if the source files in a release tarball have
not been modified has not been robust enough in cases where people first
run cmake to generate the build directory and then later change files in
the source tree.

The build has now been changed to be more in line with the development
builds, where checking for modifications is happening in all cases.

Fixes #3302

Change-Id: Id54c529bfbe51191ed5262d8da05897b2f53c057