Add CMake example

cmake-example/cmake/compile_flags.cmake

@@ -0,0 +1,15 @@
+# Note that functions are also prefixed with the project name to prevent
+# collisions.
+function(mylib_cxx_flags target)
+  # Instead of setting a specific standard directly, we use the *compile
+  # features* to require (at least) C++17 standard.
+  target_compile_features(${target} PRIVATE cxx_std_17)
+
+  # Furthermore, we turn off compiler extensions.
+  set_target_properties(${target} PROPERTIES CXX_EXTENSIONS OFF)
+
+  # We enable some warnings, although only if we know the compiler actually
+  # supports these flags. The `$<...>` syntax is a *generator expression*.
+  target_compile_options(${target} PRIVATE
+    $<$<CXX_COMPILER_ID:GNU,Clang,AppleClang>:-Wall -Wextra -pedantic>)
+endfunction()