Backport the check_mul_overflow_size_t function from this upstream commit:

commit 2e0bbbfbf95fc9e22692e93658a6fbdd2d4554da

Author: Dennis Wölfing <denniswoelfing@gmx.de>

Date:   Tue May 30 18:26:19 2017 -0300

    Add reallocarray function

diff --git a/malloc/malloc-internal.h b/malloc/malloc-internal.h

index b830d3f58fe74ca3..6ffa091ba3292901 100644

--- a/malloc/malloc-internal.h

+++ b/malloc/malloc-internal.h

@@ -28,5 +28,24 @@ void __malloc_fork_unlock_parent (void) internal_function attribute_hidden;

 /* Called in the child process after a fork.  */

 void __malloc_fork_unlock_child (void) internal_function attribute_hidden;

+/* Set *RESULT to LEFT * RIGHT.  Return true if the multiplication

+   overflowed.  */

+static inline bool

+check_mul_overflow_size_t (size_t left, size_t right, size_t *result)

+{

+#if __GNUC__ >= 5

+  return __builtin_mul_overflow (left, right, result);

+#else

+  /* size_t is unsigned so the behavior on overflow is defined.  */

+  *result = left * right;

+  size_t half_size_t = ((size_t) 1) << (8 * sizeof (size_t) / 2);

+  if (__glibc_unlikely ((left | right) >= half_size_t))

+    {

+      if (__glibc_unlikely (right != 0 && *result / right != left))

+        return true;

+    }

+  return false;

+#endif

+}

 #endif /* _MALLOC_PRIVATE_H */