cmake CXX_HAVE_SIGN_CONVERSION examples

mysql/mysql-router src/routing/CMakeLists.txt :65 

check_cxx_compiler_flag("-Wsign-conversion" CXX_HAVE_SIGN_CONVERSION)

mysql/mysql-router src/routing/tests/CMakeLists.txt :41 

check_cxx_compiler_flag("-Wsign-conversion" CXX_HAVE_SIGN_CONVERSION)