Update changelog for 1.4.0-insiders3. (#7565)

* Update changelog for 1.4.0-insiders3.

Author: sean-mcmanus

Extension/CHANGELOG.md

@@ -1,13 +1,27 @@
 # C/C++ for Visual Studio Code Change Log
 
+## Version 1.4.0-insiders3: May 24, 2021
+### Enhancements
+* Add `private` or `protected` scope labels to class symbols. [#7120](https://github.com/microsoft/vscode-cpptools/issues/7120)
+* Improvements to the C++ "Getting Started" walkthrough. [PR #7554](https://github.com/microsoft/vscode-cpptools/pull/7554)
+
+### Bug Fixes
+* Fix bitness detection for compilers targeting esp32. [#7034](https://github.com/microsoft/vscode-cpptools/issues/7034)
+* Fix issue with cpptools process lingering when no longer needed.  [#7262](https://github.com/microsoft/vscode-cpptools/issues/7262)
+* Fix enabling of the `ms_extensions` flag for clang on Windows. [#7529](https://github.com/microsoft/vscode-cpptools/issues/7529)
+* Fix `autocompleteAddParentheses` with no argument const/non-const overloads and deduction guides. [#7540](https://github.com/microsoft/vscode-cpptools/issues/7540), [#7541](https://github.com/microsoft/vscode-cpptools/issues/7541)
+* Fix clang-format failure on macOS 10.13 or older. [#7561](https://github.com/microsoft/vscode-cpptools/issues/7561)
+* Prevent 'Configuration Warnings' output when a custom configuration provider omits optional fields.
+* Prevent 'Configuration Warnings' caused by corrections to auto-detected default configuration values.
+
 ## Version 1.4.0-insiders2: May 17, 2021
 ### New Features
 * Add a C++ walkthrough to the "Getting Started" page. [#7273](https://github.com/microsoft/vscode-cpptools/issues/7273)
   * Currently, it's only usable when `"workbench.welcomePage.experimental.extensionContributions": true` is set with VS Code Insiders.
 
 ### Bug Fixes
 * Fix an incorrect IntelliSense error with object initialization. [#3212](https://github.com/microsoft/vscode-cpptools/issues/3212)
-* Fix macros getting undefined when duplicate `#include` are used. [#5182](https://github.com/microsoft/vscode-cpptools/issues/5182], [#7270](https://github.com/microsoft/vscode-cpptools/issues/7270)
+* Fix macros getting undefined when duplicate `#include` are used. [#5182](https://github.com/microsoft/vscode-cpptools/issues/5182), [#7270](https://github.com/microsoft/vscode-cpptools/issues/7270)
 * Fix IntelliSense crash with `#pragma GCC target`. [#6698](https://github.com/microsoft/vscode-cpptools/issues/6698), [#7377](https://github.com/microsoft/vscode-cpptools/issues/7377)
 * Fix completion at the end of a file. [#7472](https://github.com/microsoft/vscode-cpptools/issues/7472)
 * Fix completion of constructors. [#7505](https://github.com/microsoft/vscode-cpptools/issues/7505)