Fix static analyzer warnings

The static analyzer was complaining that we were potentially leaking
memory here (in `ASSERT_NE(ptr, nullptr)` after `new (char)`). This
wasn't correct, but it's also not possible for `new` to return nullptr
without std::nothrow.

In any case, swap to direct calls to `::operator new`, since it looks
like this test explicitly wants calls to `::operator new` to be emitted
(which the C++ standard doesn't guarantee for all `new` expressions).

Bug: 27101951
Test: mma; static analyzer warnings are gone. Also ran
memunreachable_test on marlin; no failures.
Change-Id: Ia740e41079f263040da978ba1ccc71c9c39f53fd

libmemunreachable/tests/DisableMalloc_test.cpp

@@ -73,15 +73,18 @@ TEST_F(DisableMallocTest, deadlock_allocate) {
 TEST_F(DisableMallocTest, deadlock_new) {
   ASSERT_DEATH(
       {
-        char* ptr = new (char);
+        // C++ allows `new Foo` to be replaced with a stack allocation or merged
+        // with future `new Foo` expressions, provided certain conditions are
+        // met [expr.new/10]. None of this applies to `operator new(size_t)`.
+        void* ptr = ::operator new(1);
         ASSERT_NE(ptr, nullptr);
-        delete (ptr);
+        ::operator delete(ptr);
         {
           alarm(100ms);
           ScopedDisableMalloc disable_malloc;
-          char* ptr = new (std::nothrow)(char);
+          void* ptr = ::operator new(1);
           ASSERT_NE(ptr, nullptr);
-          delete (ptr);
+          ::operator delete(ptr);
         }
       },
       "");
@@ -90,14 +93,12 @@ TEST_F(DisableMallocTest, deadlock_new) {
 TEST_F(DisableMallocTest, deadlock_delete) {
   ASSERT_DEATH(
       {
-        char* ptr = new (char);
+        void* ptr = ::operator new(1);
         ASSERT_NE(ptr, nullptr);
         {
           alarm(250ms);
           ScopedDisableMalloc disable_malloc;
-          delete (ptr);
-          // Force ptr usage or this code gets optimized away by the arm64 compiler.
-          ASSERT_NE(ptr, nullptr);
+          ::operator delete(ptr);
         }
       },
       "");