* [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

* 去掉对stl的依赖

* 头文件名，push_back改正

* 去掉构造托管

* 好像是折腾

* data 的返回改为指针，非指针引用

* resize一处写错

* stdint

* 加入c_str

* 改文件名为小写

* NCNN_SIMPLESTL option

* simplestl default to OFF

* Update linux-x64-cpu-gcc.yml

* Update linux-x64-cpu-gcc.yml

* Update linux-x64-cpu-clang.yml

* drop functional header

* arm32 arm64 simplestl ci

* 修改一处内存泄漏, 去掉编译器警告

* resize时默认量的bug

Co-authored-by: nihuini <nihuini@tencent.com>
Co-authored-by: nihui <shuizhuyuanluo@126.com>

* Fix warning C4244 in src/layer/convolution.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/convolution_sgemm_int8.h

C4244: 'initializing': conversion from 'double' to 'int', possible loss of data

* Fix warning C4244 in src/layer/deconvolution.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/elu.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4267 in src/layer/embed.cpp

C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data

* Fix warning C4244 in src/layer/exp.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/innerproduct.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/log.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data
C4244: 'initializing': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/lrn.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/mvn.cp

C4244: 'initializing': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/power.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warnings C4244 and C4267 in src/layer/proposal.cpp

C4244: 'initializing': conversion from 'double' to 'float', possible loss of data
C4244: 'initializing': conversion from 'double' to 'int', possible loss of data
C4267: 'argument': conversion from 'size_t' to 'int', possible loss of data
C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data

* Fix warning C4244 in src/layer/reduction.cpp

C4244: 'return': conversion from 'double' to 'T', possible loss of data

* Fix warning C4244 in src/layer/tanh.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/binaryop.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warnings C4244 and C4267 in src/layer/unaryop.cpp

C4244: 'return': conversion from 'double' to 'T', possible loss of data
C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data

* Fix warning C4244 in src/layer/x86/convolutiondepthwise_3x3_int8.h

C4244: 'initializing': conversion from 'double' to 'int', possible loss of data

std::{unary|binary}_function<> are deprecated in C++11 and removed in C++17.

Actually, these were unnecessary in general. In the C++98/03 era, many user-
defined function object classes derived from these base classes in an attempt
to imitate STL conventions. However, STL containers and algorithms have never
required such inheritance (or the typedefs that they provide). Only the
function object adaptors (like bind1st()) needed such typedefs. Currently,
there are no uses of function object adapters in our codebase, so we can
eliminate the inheritance completely.

* [WIP] add reduce op support for onnx

* extend reduction to support 1,2-dim reduction and keepdims

* fix compile error

* split type to 3 flags && split keepdims to another function

bug