update c api for custom allocator datareader modelbin and layer registration, add cookie userdata to layer

* package openmp and glslang together
* find glslang targets in lib64
* define version string
* update moltenvk

* fix compiling failure on cxx14

* fix compile failure when NCNN_PIXEL off

* do not export pixel api when NCNN_PIXEL off

* disable squeezenet test when NCNN_PIXEL off

* do not build ncnn2table and examples when NCNN_PIXEL off

* make cmakedefine header independent

* restore platform.h.in
Co-authored-by: Nnihui <shuizhuyuanluo@126.com>
Co-authored-by: Nnihuini <nihuini@tencent.com>

Fixed compile warnings for gcc linux build. [-Wunused-parameter]  [-Wunused-but-set-variable] (#2198)