use haswell as default arch

CMakeLists.txt

@@ -156,7 +156,7 @@ add_subdirectory(src/kem/sike)
 if(${ARCH} STREQUAL "ARCH_x86_64")
 
 set(CMAKE_C_FLAGS
-  "${CMAKE_C_FLAGS} -march=native -mtune=native")
+  "${CMAKE_C_FLAGS} -march=haswell")
 set(SRC_COMMON_AVX2
   src/common/keccak4x/KeccakP-1600-times4-SIMD256.c
 )