CMake: execute_process doesn't print any output

Summary

execute_process() function in CMake does not print any output in General Messages pane in Qt Creator. 

This bug is especially vexing when using  CMake-Conan wrapper. Internally it uses execute_process() to invoke "conan install" which builds project dependencies. It can take a long time when using big libraries, during which it seems the "conan install" process has frozen.

Steps to reproduce

Create CMakeLists.txt: 

cmake_minimum_required(VERSION 3.0)
message(STATUS "Executing custom process:")
execute_process(COMMAND echo "This is the printed executed command.")

Run in console:

mkdir build && cd build
cmake ..

You will see in the output:

-- Executing custom process:
This is the printed executed command.

Open the project in Qt Creator and build it.

Expected result

General Messages pane should contain:

-- Executing custom process:
This is the printed executed command.

Actual result

General Message pane contains 

-- Executing custom process:

but does not contain

This is the printed executed command.