How to build android library(.a) with unreal4 source

There are android library(.a) in installed engine folder. But I didn’t have the library(.a) after building the engine source. There is only UE4Game-Android-Shipping-armv7-es2.so in the folder after building. How can I build the library(.a) like UE4-Core-Android-Shipping-armv7-es2.a?

I found the solution. -precompile.