Changes

gen_makefile: --targets: fix subdir projects

Some projects are in subdirectories of git repositories, such as
simtrace2_host, or osmocom-bb_layer23. When filtering the targets to be
added to the Makefile, we must also add the main projects of such
projects in subdirectories, so Makefile rules like the following work:

  .make.simtrace2_host.clone: .make.simtrace2.clone

Fix for:
  make: *** No rule to make target '.make.simtrace2.clone', needed by '.make.simtrace2_host.clone'.  Stop.

Fixes: 1d13c9d7 ("gen_makefile: add --targets")
Change-Id: I136f0d9cd982653b109005aeb35885b6f015eec8