Minor refactoring of custom exception stacktrace interface

include/exception

@@ -105,29 +105,23 @@ class _LIBCPP_EXCEPTION_ABI exception
 public:
     _LIBCPP_INLINE_VISIBILITY exception() _NOEXCEPT
     {
-#ifdef STD_EXCEPTION_HAS_STACK_TRACE
+#if defined(STD_EXCEPTION_HAS_STACK_TRACE)
         capture();
 #endif
     }
     _LIBCPP_INLINE_VISIBILITY exception(const exception&) _NOEXCEPT = default;
 
     virtual ~exception() _NOEXCEPT;
     virtual const char* what() const _NOEXCEPT;
-#ifdef STD_EXCEPTION_HAS_STACK_TRACE
+#if defined(STD_EXCEPTION_HAS_STACK_TRACE)
     /// This is ClickHouse patch to libc++. It breaks ABI, so you cannot link your code with any C++ library
     /// that has any std::exception-related symbols exported and was built without this patch.
-    void ** const get_stack_trace_frames() const _NOEXCEPT { return const_cast<void**>(frames); }
-    int get_stack_trace_size() const _NOEXCEPT { return size; }
-    void set_stack_trace(void ** frames_, int size_) _NOEXCEPT
-    {
-        size = size_;
-        for (int i = 0; i < size; ++i)
-            frames[i] = frames_[i];
-    }
+    void * const * get_stack_trace_frames() const _NOEXCEPT { return frames; }
+    size_t get_stack_trace_size() const _NOEXCEPT { return size; }
 private:
-    static constexpr int capacity = 32;
+    static constexpr size_t capacity = 32;
     void * frames[capacity];
-    int size = 0;
+    size_t size = 0;
     void capture() _NOEXCEPT
     {
         size = unw_backtrace(frames, capacity);