feat(c-api) Start implementing wasm_target_t, wasm_triple_t and wasm_cpu_features_t.

lib/c-api/src/wasm_c_api/macros.rs

@@ -467,16 +467,19 @@ macro_rules! wasm_declare_own {
 
 #[macro_export]
 macro_rules! c_try {
-    ($expr:expr) => {{
+    ($expr:expr; otherwise $return:expr) => {{
         let res: Result<_, _> = $expr;
         match res {
             Ok(val) => val,
             Err(err) => {
                 crate::error::update_last_error(err);
-                return None;
+                return $return;
             }
         }
     }};
+    ($expr:expr) => {{
+        c_try!($expr; otherwise None)
+    }};
     ($expr:expr, $e:expr) => {{
         let opt: Option<_> = $expr;
         c_try!(opt.ok_or_else(|| $e))