Vendor dependencies for 0.3.0 release

vendor/objc-sys/extern/exception.m

@@ -0,0 +1,22 @@
+// Don't include any headers, cross compilation is difficult to set up
+// properly in such situations.
+
+/// We're linking to `libobjc` in build.rs, so this should be available.
+///
+/// See <https://clang.llvm.org/docs/AutomaticReferenceCounting.html#arc-runtime-objc-retain>.
+id objc_retain(id value);
+
+/// Unsure how C name resolution works, so we make sure to version this symbol.
+///
+/// Return `unsigned char` since it is guaranteed to be `u8` on all platforms.
+unsigned char rust_objc_sys_0_3_try_catch_exception(void (*f)(void *), void *context, id *error) {
+    @try {
+        f(context);
+        return 0;
+    } @catch (id exception) {
+        // The exception is retained while inside the `@catch` block, but is
+        // not guaranteed to be so outside of it; so hence we must do it here!
+        *error = objc_retain(exception);
+        return 1;
+    }
+}