[libc] fuzz test for heap_sort (#100826)

Made a fuzz test for heap_sort based off of qsort_fuzz implementation

libc/fuzzing/stdlib/CMakeLists.txt

@@ -6,6 +6,14 @@ add_libc_fuzzer(
     libc.src.stdlib.qsort
 )
 
+add_libc_fuzzer(
+  heap_sort_fuzz
+  SRCS
+    heap_sort_fuzz.cpp
+  DEPENDS
+    libc.src.stdlib.qsort_util
+)
+
 add_libc_fuzzer(
   atof_differential_fuzz
   SRCS

libc/fuzzing/stdlib/heap_sort_fuzz.cpp

@@ -0,0 +1,49 @@
+//===-- heap_sort_fuzz.cpp ------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// Fuzzing test for llvm-libc heap_sort implementation.
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/macros/config.h"
+#include "src/stdlib/heap_sort.h"
+#include <stdint.h>
+
+static int int_compare(const void *l, const void *r) {
+  int li = *reinterpret_cast<const int *>(l);
+  int ri = *reinterpret_cast<const int *>(r);
+  if (li == ri)
+    return 0;
+  if (li > ri)
+    return 1;
+  return -1;
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+
+  const size_t array_size = size / sizeof(int);
+  if (array_size == 0)
+    return 0;
+
+  int *array = new int[array_size];
+  const int *data_as_int = reinterpret_cast<const int *>(data);
+  for (size_t i = 0; i < array_size; ++i)
+    array[i] = data_as_int[i];
+
+  auto arr = LIBC_NAMESPACE::internal::Array(
+      reinterpret_cast<uint8_t *>(array), array_size, sizeof(int), int_compare);
+
+  LIBC_NAMESPACE::internal::heap_sort(arr);
+
+  for (size_t i = 0; i < array_size - 1; ++i)
+    if (array[i] > array[i + 1])
+      __builtin_trap();
+
+  delete[] array;
+  return 0;
+}