Rollup merge of #123633 - bjorn3:unsupported_command_data, r=jhpratt

Store all args in the unsupported Command implementation

This allows printing them in the Debug impl as well as getting them again using the get_args() method. This allows programs that would normally spawn another process to more easily show which program they would have spawned if not for the fact that the target doesn't support spawning child processes without requiring intrusive changes to keep the args. For example rustc compiled to wasi will show the full linker invocation that would have been done.

Author: matthiaskrgr