add WITH_LTO option to disble lto on compile time

cmake/enable_lto.cmake

@@ -1,10 +1,16 @@
 # -flto
 include(CheckIPOSupported)
-check_ipo_supported(RESULT IPO_ENABLED OUTPUT ipo_error)
+option(WITH_LTO "enable lto on compile time" ON)
-if(IPO_ENABLED)
+if(WITH_LTO)
-  message(STATUS "LTO enabled")
+  check_ipo_supported(RESULT IPO_ENABLED OUTPUT ipo_error)
+  if(IPO_ENABLED)
+    message(STATUS "LTO enabled")
+  else()
+    message(WARNING "LTO not supported by compiler: ${ipo_error}")
+  endif()
 else()
-  message(WARNING "LTO not supported by compiler: ${ipo_error}")
+  message(STATUS "LTO disabled")
+  set(IPO_ENABLED OFF)
 endif()
 
 function(enable_lto)