add default option to avoid building example executables

CMakeLists.txt

@@ -1,6 +1,8 @@
 cmake_minimum_required(VERSION 3.10)
 project(toddcox-faster)
 
+option(TC_BUILD_EXAMPLE "Build example executables" OFF)
+
 add_library(tc STATIC
         src/groups.cpp
         src/solve.cpp
@@ -8,4 +10,6 @@ add_library(tc STATIC
 
 target_include_directories(tc PUBLIC include)
 
-add_subdirectory(example)
+if (TC_BUILD_EXAMPLE)
+    add_subdirectory(example)
+endif ()