`ModelicaInternal_temporaryFileName`: Replace `tmpnam` with `mkstemp`

[AnHeuermann]

Issue

Function tmpnam in ModelicaInternal.c#L760 is so notoriously unsafe that the C standard warns against it:

libModelicaExternalC.a(ModelicaInternal.c.o): in function `ModelicaInternal_temporaryFileName':
/path/to/ModelicaExternalC/C-Sources/ModelicaInternal.c:682:(.text+0x8cd): warning: the use of `tmpnam' is dangerous, better use `mkstemp'

Suggested Changes

Use a safer alternative

• POSIX (all Unix-like systems): mkstemp
• Windows: GetTempFileNameA

That guarantees atomic operations, uniqueness and honors temp directories set by TEMPDIR.
With the POSIX variant the right permissions are set (0600), since the data lives in a shared directory (/tmp).
On Windows usually the %LOCALAPPDATA%\Temp directory is used, which is already only readable by the user, or use an explicit ACL/DACL restrictor.

That would slightly change the behavior to do unique name generation and file generation in one atomic step instead of returning a name to a non-existing temp file (which is precisely the root issue of tmpnam).
If it's fine for ModelicaInternal_temporaryFileName to generate the files directly I can provide a pull request.

Deprecate ModelicaInternal_temporaryFile

If it's not okay that the behavior would change I would suggest to add a new internal function ModelicaInternal_temporaryFile and deprecate ModelicaInternal_temporaryFileName in favor of it and remove it in a future version.

Related issues

See also #3647.