windows build `build_cpu_nms.sh` need to change setting.

[Animadversio]

This is a fantastic package!

I noted that trying to build_cpu_nms on Windows system will throw an compilation error about '/Wno-cpp'

cl : Command line error D8021 : invalid numeric argument '/Wno-cpp'

This is related to this issue mentioned in cocodataset
cocodataset/cocoapi#51

The quick fix to it is to change L47 in FaceBoxes\utils\build.py
from extra_compile_args=["-Wno-cpp", "-Wno-unused-function"],#
to extra_compile_args={'gcc': ['/Qstd=c99']},#["-Wno-cpp", "-Wno-unused-function"],