CMake "Atomic" IMPORTED target should have a namespace

The Qt6 CMake files define a target called "Atomic". CMake IMPORTED targets should have a namespace so that

1) You don't clash with other SDKs (consider the problematic X11 "#define Status" )
2) CMake knows that the name refers to a target, not a file on the filesystem. See https://cmake.org/cmake/help/latest/policy/CMP0028.html

This target and any others which do not have a namespace should be renamed to have a double colon in the name. For example in this case, Qt6::StdAtomic.