os.tempfolder is broken on Windows

[sfan5]

Reproduced on Wine, but it looks like the problem happens on real Windows too.

With some debug output added inside os.tempfolder and dlg_contentstore.lua:

filetocheck = '\s1d.'
randname = 'MTTempModFolder_1185'
screenshot_dir = '\MTTempModFolder_1185'
2018-06-10 18:50:49: ERROR[Main]: GUIEngine: execution of menu script failed: Failed to load and run script from Z:\var\tmp\minetest-0.5.0-90acb9b-win64\bin\..\builtin\init.lua:
2018-06-10 18:50:49: ERROR[Main]: ...acb9b-win64\bin\..\builtin\mainmenu\dlg_contentstore.lua:24: assertion failed!

This was caused by a2de439, @nOOb3167

[Fixer-007]

Can confirm this on win7

[nOOb3167]

https://blogs.msdn.microsoft.com/vcblog/2014/06/18/c-runtime-crt-features-fixes-and-breaking-changes-in-visual-studio-14-ctp1/

tmpnam Generates Usable File Names: In previous versions, the tmpnam and tmpnam_s functions generated file names in the root of the drive (e.g. \sd3c.). These functions now generate usable file name paths in a temporary directory.

The '\s1d.' filename format is a tmpnam defect fixed somewhere in year 2014.
I think VS 2012 and earlier do not support enough C++11 standard to build minetest.
So I assume you are using Visual Studio 2013 to build?
Visual Studio 2015, 2017, or higher should be safe.

What toolchain produces the defective builds?
In worst case scenario even MinGW build could be affected, if they tried to be bug-compatible with older visual studio.

[SmallJoker]

So I assume you are using Visual Studio 2013 to build?

They're using GCC/MinGW to cross compile it for Windows (we have a buildbot script for that). What we need here is glue to provide compatibility for MSVC >= 2015 and MinGW.

[SmallJoker]

#7443 merged.