rust: build: move rustc_args.py invocation to qemu-api crate

Only qemu-api needs access to the symbols in config-host.h.  Remove
the temptation to use them elsewhere by limiting the --cfg arguments to
the qemu-api crate.

Per-crate invocation of the script will also be needed to add --check-cfg
options for each crate's features (when more complex, build-time
configurable devices are added in the future).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2 files changed