cmake HAS_IPO_FLAG examples

xtensor-stack/xtensor-blas benchmark/CMakeLists.txt :49 

CHECK_CXX_COMPILER_FLAG("-ipo" HAS_IPO_FLAG)

xtensor-stack/xtensor-python benchmark/CMakeLists.txt :48 

CHECK_CXX_COMPILER_FLAG("-ipo" HAS_IPO_FLAG)

xtensor-stack/xtensor benchmark/CMakeLists.txt :58 

CHECK_CXX_COMPILER_FLAG("-ipo" HAS_IPO_FLAG)