Fix CMakeLists.txt

Author: chavid

exercises/race/CMakeLists.txt

@@ -15,8 +15,10 @@ target_link_libraries( racing PRIVATE Threads::Threads )
 # Create the "solution executable".
 add_executable( racing.sol1 EXCLUDE_FROM_ALL "solution/racing.sol1.cpp" )
 target_link_libraries( racing.sol1 PRIVATE Threads::Threads )
+add_custom_target( solution1 )
 add_dependencies( solution1 racing.sol1 )
 add_executable( racing.sol2 EXCLUDE_FROM_ALL "solution/racing.sol2.cpp" )
 target_link_libraries( racing.sol2 PRIVATE Threads::Threads )
+add_custom_target( solution2 )
 add_dependencies( solution2 racing.sol2 )
 add_dependencies( solution solution1 solution2 )