Re-add --rust-target to replace --unstable-rust

Instead of specifying whether or not to use stable, specify the Rust
release to support (one of several stable/beta releases or nightly).
The `--unstable-rust` option is still accepted and implies nightly.

The definitions of `RustTarget` and `RustFeatures` are created with
macros.

For each test that uses unions, there is a version that uses the latest
stable and 1.0.

This also fixes the bug where unions were generated with non-Copy
fields.

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/headers/union_fields.hpp b/tests/headers/union_fields.hpp
index cc8fcbe4..dd15d741 100644
--- a/tests/headers/union_fields.hpp
+++ b/tests/headers/union_fields.hpp
@@ -1,5 +1,5 @@
 // bindgen-flags: --with-derive-hash
-//
+
 typedef union {
   int mInt;
   float mFloat;