AOSP compilation issue on Hikey 970

I followed steps of official guild to compile AOSP for my Hikey 970; but the compilation failed because of this issue:

build/make/core/Makefile:28: error: overriding commands for target `out/target/product/hikey970/system/vendor/lib/libc_secshared.so’, previously defined at build/make/core/base_rules.mk:418

Anybody know how to solve this problem?