C++: Add failing tests.

Author: MathiasVP

cpp/ql/test/query-tests/Likely Bugs/Memory Management/ReturnStackAllocatedMemory/test.cpp

@@ -229,4 +229,23 @@ int* id(int* px) {
 void f() {
   int x;
   int* px = id(&x); // GOOD
+}
+
+void *alloca(size_t);
+
+void* test_alloca() {
+	void* p = alloca(10);
+	return p; // BAD [NOT DETECTED]
+}
+
+char *strdupa(const char *);
+char *strndupa(const char *, size_t);
+
+char* test_strdupa(const char* s) {
+	return strdupa(s); // BAD [NOT DETECTED]
+}
+
+void* test_strndupa(const char* s, size_t size) {
+	char* s2 = strndupa(s, size);
+	return s2; // BAD [NOT DETECTED]
 }