* [build] add toolchain file w/o stdcxx dependency

* [build] link m and gcc lib explicitly

* [ncnn] complete simple stl impl

* [ncnn] adapt for ncnn simplestl

* [test] adapt for ncnn simplestl

* [ncnn] fix missing algorithm and list when simplestl disabled

* [ncnn] fix guard for operator new and delete

* [style] fix the code style

* [build] fix build failed on darwin and emscripten

* [ci] do not import cxx to avoid operator conflict

* [ncnn] add temporary partial_sort impl using bubble sort

heap sort should be used for better perf.

* [ncnn] add std greater and less function

* [ncnn] fix placement new operator overload

* [ncnn] add operator delete with size info

* [build] disable exception, rtti, example and tools when simplestl on

* [build] add toolchain for arm simplestl

* [build] add toolchain for aarch64 simplestl

* [ncnn] move initializer to constructor

* [ncnn] use deteiled type instead of auto

* [ncnn] use plain lib name in target_link_libraries

* give hint for VUKLAN_SDK on Windows

note:

1. tested with vulkan sdk 1.2.148.0, the .exe installer will automatically set VULKAN_SDK env var in System Config after installation.

2. only tested with VS2017. cmake 3.6.3 not support VS2017 since it is
released in 2016.

* fix cmake find vulkan on windows

* fix macos cmake find vulkan

Co-authored-by: Restyled.io <commits@restyled.io>
Co-authored-by: nihui <shuizhuyuanluo@126.com>