[CMake] Disable release mode for Swift
[CMake] Disable release mode for Swift

Looks like release mode is broken in the Swift support, we need to
re-land it with a proper fix.

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