Unable to launch external console on MacOS when using GDB

Type: Debugger

Describe the bug

• OS and Version: MacOS Mojave
• VS Code Version: 1.33.1
• C/C++ Extension Version:0.23.1
• Other extensions you installed (and if the issue persists after disabling them):
• A clear and concise description of what the bug is.

When trying to debug on macOS using gdb instead of lldb external console is not started, even when "externalConsole": true is set in launch.json.

To Reproduce
Please include a code sample and launch.json configuration.
Steps to reproduce the behavior:

1. Create simple hello world program like one below:

#include <iostream>
#include <string>
using namespace std;

int main()
{
	string name;
	cin >> name;
	cout << "Hello " + name << endl;
	return 0;
}

2. Create launch.json like the one here:

	{
		"name": "(gdb) Launch Mac",
		"type": "cppdbg",
		"request": "launch",
		"program": "${fileDirname}/${fileBasenameNoExtension}.out",
		"args": [],
		"stopAtEntry": false,
		"cwd": "${fileDirname}",
		"environment": [],
		"externalConsole": true,
		"MIMode": "gdb",
		"setupCommands": [
			{
				"description": "Enable pretty-printing for gdb",
				"text": "-enable-pretty-printing",
				"ignoreFailures": true
			}
		]
	}

3. Launch debugger.
4. No external input console is started, disabling user to enter name when debugging.