libiPhone-lib.a is too big after Unity build to xcode(size is about 1.1G!)

My unity version is 5.3.2p4 personal.I create an empty project and build with IL2CPP to xcode,there is a big file named libiPhone-lib.a. Even my project is empty,this file also is 1.1G! If I build with Mono2x and choose a stripping level, this file become 500M,but Mono2x don't include ARM64. How can I keep the libiPhone-lib.a in a small size and make my build both include ARMv7 & ARM64?