In cmGlobalXCodeGenerator::Generate we generate a .xcodeproj for each
directory in the tree containing a project() command. First we
iteratively use SetGenerationRoot to add "ALL_BUILD" and other targets
to each project. This leaves "CurrentProject" set to the last project
when we invoke cmGlobalGenerator::Generate, which is not the same as the
top-level project if any subdirectories invoke the project() command.
When cmGlobalGenerator::Generate reaches CreateGeneratorTargets it
constructs cmGeneratorTarget and calls ComputeTargetObjects exactly once
per target. In this context the value of CurrentProject is undefined so
we cannot pass it to GetObjectsNormalDirectory. Use "$(PROJECT_NAME)"
instead so it will adapt automatically to each project.
Also teach Tests/ObjectLibrary to cover this case.
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