Bug 243228

Schemes like "WebCore", "JavaScriptCore", etc. currently build the entire workspace _up to_ their respective framework. The idea is that it's an easy way to build a subset of the workspace up to a specific target.

However, with the switch to Make-based workspace builds, there is no longer a workflow for building a single project _without_ its dependencies. My understanding from talking to folks is that we need a way to do this, for a number of reasons:

- We have scripts that run redundantly, so a null build of the full stack is slower than a null build of a single project, sometimes by 10-15 sec.
- Sometimes an engineer is working on unrelated or staged changes in separate parts of the workspace, and doesn't want changes in one project to cause heavy rebuilds of the other project.
- It's unintuitive that running Make in a specific directory (e.g. `make -C Source/WebCore`) will build projects in other directories.

If we agree that these are workflows that we should support, then we need a way to build these projects in the workspace without their dependencies. Because Xcode doesn't allow us to control dependency resolution at runtime, I propose we turn off "Find Implicit Dependencies" in all the single-project schemes.