NCNN_VERSION_STRING enhancement

[zchrissirhcz]

Problem description

The c/c++ macro NCNN_VERSION_STRING describes the build date, and maybe change it to "source code tag / commit" is better.

Details

In the CMakeLists.txt, there is NCNN_VERSION_STRING defined.

The header file platform.h, which is generated from platform.h.in, defines NCNN_VERSION_STRING macro, which is generated from the cmake variable NCNN_VERSION_STRING.

Today( 2022.08.04), I cloned and switched to tag 20220701, build and install then use it, but get the version "20220804", feel confusing..

#include "platform.h"
#include "c_api.h"

int main()
{
    fprintf(stderr, "version: %s\n", NCNN_VERSION_STRING);
    fprintf(stderr, "ncnn_version: %s\n", ncnn_version());
    return 0;
}

Actual Output:

version: 1.0.20220804
ncnn_version: 1.0.20220804

Expected Output:

version: 1.0.202200701
ncnn_version: 1.0.20220701

Or

version: 1.0.202200701-BuildDate20220804
ncnn_version: 1.0.20220701-BuildDate20220804