[scudo] Fix c wrappers double free test. (llvm#148066)

The previous test simply tried to double free the pointer in the
EXPECT_DEATH macro. Unfortunately, the gtest infrastructure can allocate
a pointer that happens to be the previously freed pointer. Thus the free
doesn't fail since the spawned process does not attempt to free all of
the pointers allocated in the original test.

NOTE: Scudo should be checked to make sure that the TSD is not always
returning pointers in the same order they are freed. Although this
appears to be a problem with a program that only does a small number of
allocations.

Author: cferris1000

compiler-rt/lib/scudo/standalone/tests/wrappers_c_test.cpp

@@ -175,7 +175,19 @@ TEST_F(ScudoWrappersCDeathTest, Malloc) {
 
   free(P);
   verifyDeallocHookPtr(P);
-  EXPECT_DEATH(free(P), "");
+
+  // Verify a double free causes an abort.
+  // Don't simply free(P) since EXPECT_DEATH will do a number of
+  // allocations before creating a new process. There is a possibility
+  // that the previously freed P is reused, therefore, in the new
+  // process doing free(P) is not a double free.
+  EXPECT_DEATH(
+      {
+        void *Ptr = malloc(Size);
+        free(Ptr);
+        free(Ptr);
+      },
+      "");
 
   P = malloc(0U);
   EXPECT_NE(P, nullptr);