Provide a way to get initial cmake invocation arguments that were passed on the command line

Hi,

I hope this is not a duplicate.

But there does not seem to be a way to get the original command line arguments that were passed to CNake when initially configuring a project.

This will be important for Qt Android multi ABI builds.

Conceptually, we would like the user to configure Qt with something like: cmake -DFOO -DBAR=1 -DCMAKE_SYSTEM_NAME=ANDROID -DANDROID_ABIS=arm64,x86_64

and inside the top level Qt CMake project, we would manually spawn 2 processes invoking CMake in two different build directories, with the original parameters passed from the user, + some other parameters specific to the Android ABI. For that we need a way to get the list of all the initially passed in command line arguments.