test(ffi-linkage): xfail export "csym" rename (Phase 2.2)

example/1227 exposes the sx fn `sx_triple` to C under the symbol `triple_c`
via `export "triple_c"`; the companion C calls `triple_c` by that name.
RED: the define path emits the fn under its sx name (`sx_triple`) and
ignores the parsed `extern_name`, so the C reference to `triple_c` is
undefined at AOT link. The next commit consumes the rename on the define
path (gap iii) and greens it.

examples/1227-ffi-export-fn-rename.c

@@ -0,0 +1,8 @@
+#include "1227-ffi-export-fn-rename.h"
+
+// Defined on the sx side via `export "triple_c"` — a plain C-ABI symbol.
+extern int triple_c(int n);
+
+int call_triple(int n) {
+    return triple_c(n) + 1;
+}

examples/1227-ffi-export-fn-rename.h

@@ -0,0 +1,7 @@
+#ifndef SX_EXPORT_FN_RENAME_H
+#define SX_EXPORT_FN_RENAME_H
+
+// Calls back into the sx-exported `triple_c` and adds 1.
+int call_triple(int n);
+
+#endif

examples/1227-ffi-export-fn-rename.sx

@@ -0,0 +1,23 @@
+// export with a "csym" rename (FFI-linkage stream, Phase 2.2): the sx name
+// `sx_triple` is exposed to C under the symbol `triple_c` via the optional
+// symbol-name override after `export` — the define-direction mirror of
+// `extern "csym"` (1224). The companion C calls `triple_c` by that name; sx
+// `main` drives it via `call_triple`. Runs in AOT mode (see the `.aot`
+// marker) because a C->sx-by-name call cannot link against a JIT-resident
+// symbol.
+#import "modules/std.sx";
+
+#import c {
+    #include "1227-ffi-export-fn-rename.h";
+    #source "1227-ffi-export-fn-rename.c";
+};
+
+// sx-defined, exported to C under the C symbol `triple_c`.
+sx_triple :: (n: i32) -> i32 export "triple_c" {
+    return n * 3;
+}
+
+main :: () -> i32 {
+    print("call_triple(7) = {}\n", call_triple(7));
+    0
+}

examples/expected/1227-ffi-export-fn-rename.exit

@@ -0,0 +1 @@
+0

examples/expected/1227-ffi-export-fn-rename.stdout

@@ -0,0 +1 @@
+call_triple(7) = 22