call omp_set_num_threads with zero num_threads is implementation defined

Co-authored-by: nihui <nihui@users.noreply.github.com>
Co-authored-by: michaelcai <michaelcai@tencent.com>

* disable rtti and exceptions for msvc

* warnings--

* erff

* arch sse2 for 32bit build

* enable rtti for cross compiling

* vulkan-driver-loader.md
* static vulkan on apple

* complete abs, fmod and sin function in simplemath.h

* remove some unused variables in simplemath.cpp

* modify test-coverage.yml and add some functions to simplemath.cpp

* modify erf.cpp which included math.h

* include platform.h for NCNN_SIMPLEMATH definition

* move utility constants and functions in simplemath.h to simplemath.cpp

* guard simplemath functions with extern "C"

* add NCNN_EXPORT macro in simplemath.h

* include plateform.h and guard all declarations with NCNN_SIMPLEMATH

* clean unused code in test_unaryop.cpp

* guard #include <vector> with NCNN_SIMPLEMATH in benchncnn.cpp

* add 'static' to guard functions that not declarated in header file

* modify sin and cos with better implementation

---------

Co-authored-by: HonestDeng <HonestDeng@users.noreply.github.com>

* enable out elempack 8 for winograd and sgemm

* pnnx support grid_sample op

* complete the permute and gridsample operator fusion

* spilt calculation into two stages and support permute fusion

Co-authored-by: Xinyu302 <Xinyu302@users.noreply.github.com>

Signed-off-by: daquexian <daquexian566@gmail.com>

* added erf implementation

* added testcase for erf

* added onnx2ncnn support of erf