Merge topic 'dev/refactor-source-depends-in-ninja'

2583eff6 ninja: Factor out custom command order-only depends
18e478a8 ninja: Factor out target-level order-only dependencies
6fa6bedf LocalGenerator: Add a string overload for AppendFlags
01b79c63 ninja: Don't use a stringstream to build an argument list
3c640891 ninja: Use string parameters
Merge branch 'master' into next