1.first of all ,you will meet many problem no excute permisson,pls do :
chmod -R +x APQ8084/

2. build/core/base_rules.mk:130: *** external/webrtc/src/system_wrappers/source: MODULE.TARGET.STATIC_LIBRARIES.libwebrtc_system_wrappers already defined by external/webrtc/src/system_wrappers/source. Stop.

pls do:
"unset NDK_ROOT"
as Apparently there is a bug in the webrtc makefiles that causes it to ignore including STL if the NDK_ROOT environmental variable is previously defined (by ~/.bashrc, in my case). So just make sure NDK_ROOT is not defined at all when building

3. do not use shell named build.sh in APQ8084 root directory
improve compile speed by below operation:
a. modify ~/.bashrc, add "export USE_CCACHE = 1"
b. prebuilts/misc/linux-x86/ccache/ccache -M 50G

then compile:
source build/envsetup.sh;
lunch; pls choose apq8084
make -j8

How to make apq8084