anchor.diff:  cmake .. -DCMAKE_CXX_FLAGS="-DEX3"
   ----
   
  -[[set-default-flag]]
  -Set Default C++ Flags
  -^^^^^^^^^^^^^^^^^^^^^
  +## Set Default C++ Flags
   
   The default `CMAKE_CXX_FLAGS` is either empty or contains the appropriate flags
   for the build type.
  
positive.code:   * CMakeLists.txt - Contains the CMake commands you wish to run
    * main.cpp - The source file with main
  
  [[concepts]]
  Concepts
  ~~~~~~~~
  
  [[set-cpp-flag]]
  Set C++ Flag
  ^^^^^^^^^^^^
  
  Similar to the build type a C++ compiler flag can be set using the following methods.
  
  
negative.code: = Compile Flags
  :toc:
  :toc-placement!:
  
  toc::[]
  
  # Introduction
  
  CMake supports setting compile flags using the +CMAKE_C_FLAGS+ and +CMAKE_CXX_FLAGS+
  variables. Similarly linker flags can be set using the +CMAKE_LINKER_FLAGS+.
  