CMake add_custom_target adds nonexistent file to ide
CMake adds a nonexistent file named "${CMAKE_BINARY_DIR}/CMakeFiles/testtarget" to (VS2015) if the following (stripped-down) script is run.
cmake_minimum_required( VERSION 3.7.0 )
project( test_sample VERSION 0.1 LANGUAGES CXX )
add_custom_target( testtarget COMMAND dir )