translate-c: do not translate macros which use arguments as struct/union/enum names

Consider this C macro:
```c
#define FOO(x) struct x
```

Previously, translate-c did not detect that the `x` in the body referred
to the argument, so wrongly translated this code as using the
nonexistent `struct_x`. Since undefined identifiers are noticed in
AstGen, this prevents the translated file from being usable at all.

translate-c now instead detects this case and emits an appropriate
compile error in the macro's place.

1 files changed, 6 insertions, 0 deletions

diff --git a/test/translate_c.zig b/test/translate_c.zig
index 3a453b9aa8..3fad7f8fe5 100644
--- a/test/translate_c.zig
+++ b/test/translate_c.zig
@@ -4129,4 +4129,10 @@ pub fn addCases(cases: *tests.TranslateCContext) void {
         \\    }) != 0) {}
         \\}
     });
+
+    cases.add("macro using argument as struct name is not translated",
+        \\#define FOO(x) struct x
+    , &[_][]const u8{
+        \\pub const FOO = @compileError("unable to translate macro: untranslatable usage of arg `x`");
+    });
 }