Try fix some build/publish issues.

Cargo.toml

@@ -41,3 +41,4 @@ strip = "symbols"
 
 [features]
 sitk_no_build = []  # do not build all the C++ stuff, just use the rust code to make docs etc.
+copy_autocxx_src = []  # copy the generated autocxx-ffi-default-gen.rs to src for inclusion in the repo

build.rs

@@ -74,10 +74,11 @@ fn main() -> Result<(), Box<dyn Error>> {
                 cpp_string.replace_all(&cxx, "pub mod simple {\nuse crate::ffi::ToCppString;");
             write!(f, "{}", cxx)?;
         }
+        if cfg!(feature = "copy_autocxx_src") {
             fs::copy(dst.join(&cxx_file), "src/autocxx-ffi-default-gen_unfmt.rs")?;
             Command::new("rustfmt").arg(&cxx_file).status()?;
             fs::copy(dst.join(&cxx_file), "src/autocxx-ffi-default-gen.rs")?;
-
+        }
         println!("cargo:warning=merged_lib={}", merged_lib.join("build").display());
         println!("cargo:rustc-link-search={}", merged_lib.join("build").display());
         println!("cargo:rustc-link-lib=static=sitk_ffi_extra");