add native build option

CMakeLists.txt

@@ -13,6 +13,7 @@ project(${PROJECT_NAME} C CXX)
 option(USE_AVX2 "enable avx2 code" )
 option(USE_NETNS "enable networking namespace support. Linux only" )
 option(AMD_RYZEN_HACK "hack for AMD Ryzen FPU bug (support FMA3 and FMA4 in FPU, but does not show in CPUID)" )
+option(NATIVE_BUILD "optimise for host system and FPU, may not be portable" )
 if (NOT MSVC)
 option(STATIC_LINK_RUNTIME "link statically against compiler runtime, standard library and pthreads")
 endif()
@@ -157,6 +158,11 @@ if(AMD_RYZEN_HACK AND USE_AVX2)
   message(WARNING "This option may be removed in a future release. Contact your computer manufacturer for updated ROMs or microcode patches.")
 endif(AMD_RYZEN_HACK AND USE_AVX2)
 
+if(NATIVE_BUILD)
+  message(WARNING "May fail at runtime if the floating-point unit on the target system does not implement required features, some platforms will check this for you")
+  set(CRYPTO_FLAGS -march=native -mfpmath=sse -mtune=native)
+endif()
+
 add_compile_options(${OPTIMIZE_FLAGS} ${CRYPTO_FLAGS})
 
 set(CMAKE_THREAD_PREFER_PTHREAD TRUE)