C++: Add a testcase with many def/use pairs in alias analysis.

cpp/ql/test/library-tests/ir/ir/ir.cpp

@@ -2686,4 +2686,25 @@ void test(bool b)
   twice_call_use(b ? "" : "");
 }
 
+#define CONCAT(a, b) CONCAT_INNER(a, b)
+#define CONCAT_INNER(a, b) a ## b
+
+#define READ do { String CONCAT(x, __COUNTER__); } while(0)
+
+#define READ2 READ; READ
+#define READ4 READ2; READ2
+#define READ8 READ4; READ4
+#define READ16 READ8; READ8
+#define READ32 READ16; READ16
+#define READ64 READ32; READ32
+#define READ128 READ64; READ64
+#define READ256 READ128; READ128
+#define READ512 READ256; READ256
+#define READ1024 READ512; READ512
+#define READ1025 READ1024; READ
+
+void many_defs_per_use() {
+    READ1025;
+}
+
 // semmle-extractor-options: -std=c++20 --clang