Hello,
I am building ffmpeg and mp4box with the [ffmpeg-windows-build-helpers](https://github.com/rdp/ffmpeg-windows-build-helpers)
Since recently mp4box building is compromised.

I think it has something to do with a typo in the file `utils/os_file.c`.
There it says in lines 411, 422 and 877: `st.st_mtim.tv_nsec`.
I think it should say `st.st_mtime.tv_nsec`.

Could you please check and fix that? Thanks. :)

> Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!
> 
> - [X] I looked for a similar issue and couldn't find any.
> - [X] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
> - [X] I give enough information for contributors to reproduce my issue (meaningful title, github labels, platform and compiler, command-line ...). I can share files anonymously with this dropbox: https://www.mediafire.com/filedrop/filedrop_hosted.php?drop=eec9e058a9486fe4e99c33021481d9e1826ca9dbc242a6cfaab0fe95da5e5d95
> 
> Detailed guidelines: http://gpac.io/2013/07/16/how-to-file-a-bug-properly/
Building of mp4box not working
This is a GitHub Issue
repo:gpac
owner:gpac
Title : Building of mp4box not working
Issue date:

--- start body ---
Hello,
I am building ffmpeg and mp4box with the [ffmpeg-windows-build-helpers](https://github.com/rdp/ffmpeg-windows-build-helpers)
Since recently mp4box building is compromised.

I think it has something to do with a typo in the file `utils/os_file.c`.
There it says in lines 411, 422 and 877: `st.st_mtim.tv_nsec`.
I think it should say `st.st_mtime.tv_nsec`.

Could you please check and fix that? Thanks. :)

> Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!
> 
> - [X] I looked for a similar issue and couldn't find any.
> - [X] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
> - [X] I give enough information for contributors to reproduce my issue (meaningful title, github labels, platform and compiler, command-line ...). I can share files anonymously with this dropbox: https://www.mediafire.com/filedrop/filedrop_hosted.php?drop=eec9e058a9486fe4e99c33021481d9e1826ca9dbc242a6cfaab0fe95da5e5d95
> 
> Detailed guidelines: http://gpac.io/2013/07/16/how-to-file-a-bug-properly/
--- end body ---

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