Rename file "aux.c" because it is a reserved filename on Windows

[fvilante]

Improve Multi-Platform Support

The file 'tests/simulate/time/aux.c' use a reserved filename on Microsoft Windows systems.

Therefore you will experience an error when cloning this repository on Windows.

This error also propagates to downstream users of other languages like in this case rust_avr_libc. The building tools also does not work because that.

Just renaming the filename will solve the problem and make the library platform agnostic.

related: #889

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╰─❯ git clone https://github.com/avrdudes/avr-libc.git
Cloning into 'avr-libc'...
remote: Enumerating objects: 22589, done.
remote: Counting objects: 100% (576/576), done.
remote: Compressing objects: 100% (115/115), done.
remote: Total 22589 (delta 488), reused 536 (delta 461), pack-reused 22013
Receiving objects: 100% (22589/22589), 9.85 MiB | 5.59 MiB/s, done.
Resolving deltas: 100% (18329/18329), done.
error: invalid path 'tests/simulate/time/aux.c'
fatal: unable to checkout working tree
warning: Clone succeeded, but checkout failed.
You can inspect what was checked out with 'git status'
and retry with 'git restore --source=HEAD :/'

[sprintersb]

Closed as dup of #889.