Fix header target membership
Fix header target membership

libllbuild.dylib should have the same headers as the framework, because
they are important to TAPI even if otherwise unnecessary. Similarly,
swift-Ninja should not have any headers because it does not vend those
APIs; it only exports the APIs from the sole Swift file it builds.

apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild