Add a thiscall_abi test for stable Rust 1.73.

Author: rodrigorc

bindgen-tests/tests/expectations/tests/win32-thiscall_1_73.rs

@@ -0,0 +1,7 @@
+// bindgen-flags: --rust-target=1.73 --raw-line '#![cfg(target = "i686-pc-windows-msvc")]' -- --target=i686-pc-windows-msvc
+
+class Foo {
+  public:
+    void test();
+    int test2(int var);
+};