Adam Strzelecki authored Jun 13, 2014 and Brad King committed Jun 16, 2014

It may happen that CMake include is an explicit dependency for some command,
while all CMake includes are set phony in WriteTargetRebuildManifest, this may
lead to duplicate phony generate rules which causes ninja warnings.

We need to remove implicit CMake includes in WriteUnknownExplicitDependencies.

This fixes FindCUDA ninja warnings.