Fix platform checks, add initial gn args,
use shared library template for gn to get all
the linker objects. This is just debug build.

Task-number: QTBUG-77931
Change-Id: I9b3f7d3440aec66433ed19f4976e14506fba45dd
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>