cmake CXX_HAVE_SHADOW examples

mysql/mysql-router src/routing/CMakeLists.txt :60 

check_cxx_compiler_flag("-Wshadow" CXX_HAVE_SHADOW)

mysql/mysql-router src/routing/tests/CMakeLists.txt :34 

check_cxx_compiler_flag("-Wshadow" CXX_HAVE_SHADOW)

mysql/mysql-router src/x_protocol/CMakeLists.txt :56 

check_cxx_compiler_flag("-Wshadow" CXX_HAVE_SHADOW)