Move Linux build rule to its own folder, update to v5.4.2

The Linux build rule was previously in //third_party/ which meant it was
built in the same folder as other third-party projects. Move its build
rule to its folder to avoid clashes.

Also update Linux to v5.4.2 and update submodule refs.

Change-Id: I32598092c3ef400677ccdb22d0b92f68de113d39
8 files changed