Add zstd unsound both branches dead test

tests/regression/03-practical/31-zstd-cctxpool-blobs.c

@@ -0,0 +1,29 @@
+#include <stdlib.h>
+#include <pthread.h>
+
+struct ZSTD_CCtx_s {
+  int bmi2;
+};
+
+typedef struct ZSTD_CCtx_s ZSTD_CCtx;
+
+typedef struct {
+  ZSTD_CCtx* cctx[1];
+} ZSTDMT_CCtxPool;
+
+void *t_fun(void *arg) {
+  return NULL;
+}
+
+int main() {
+  pthread_t id;
+  pthread_create(&id, NULL, t_fun, NULL); // enter multithreaded
+
+  ZSTDMT_CCtxPool* const cctxPool = calloc(1, sizeof(ZSTDMT_CCtxPool));
+  cctxPool->cctx[0] = malloc(sizeof(ZSTD_CCtx));
+  if (!cctxPool->cctx[0]) // TODO NOWARN
+    __goblint_check(1); // TODO reachable
+  else
+    __goblint_check(1); // TODO reachable
+  return 0;
+}