Don't fail if a target of type NONE has a NOTICE file present

Targets of type NONE are used extensively in Android makefiles which have been
auto-generated from gyp build files. The gyp generator uses such targets to
represent gyp targets which don't produce an output file. Typically, many such
targets exist in a single Android makefile.

We use a generated Android makefile for Chromium. This project has a NOTICE
file, intended to be installed with a SHARED_LIBRARY target. However, the build
fails when processing the targets of type NONE, as it does not know where
to install the NOTICE file.

This change causes the NOTICE to be ignored in this case, rather than failing
the build.

Change-Id: I70cf9a406e4a1c932f8a734f53491f7c5281ee17