Add minimized testcase from both apron branches dead without threadflag

Author: sim642

tests/regression/46-apron2/24-pipeline-no-threadflag.c

@@ -0,0 +1,16 @@
+// SKIP PARAM: --set ana.activated[+] apron --set ana.activated[-] threadflag
+// Minimized from sv-benchmarks/c/systemc/pipeline.cil-1.c
+#include <assert.h>
+
+int main_clk_pos_edge;
+int main_in1_req_up;
+
+int main()
+{
+  // main_clk_pos_edge = 2; // TODO: uncomment to unskip apron test
+  if (main_in1_req_up == 1) // TODO: both branches are dead
+    assert(0); // FAIL (unreachable)
+  else
+    assert(1); // reachable
+  return (0);
+}