tuxmake does not respect default ccache CCACHE_DIR

***In GitLab by @krzkoz on Jun 17, 2025, 12:11 GMT+1:***

By default ccache v4.10.2 has ccache in .cache/ccache (at least on Ubuntu 24.10, not Windows - important further).

tuxmake ignores it completely and sets up a new one in ~/.ccache, overriding existing default one. It seems it assumes CCACHE_DIR has a fixed value, but the man page:

> On non-Windows systems, the default is $HOME/.ccache if such a directory exists, otherwise $XDG_CACHE_HOME/ccache if XDG_CACHE_HOME is set, otherwise $HOME/Library/Caches/ccache (macOS) or $HOME/.config/ccache (other systems).

tuxmake 1.29.3

```
$ cat ~/.config/tuxmake/default
--wrapper=ccache
--build=out/
--verbose
```
```
$ printenv | grep CCACHE
USE_CCACHE=1
```

*Migrated from GitLab: https://gitlab.com/Linaro/tuxmake/-/issues/225*

Start by tracing tuxmake's ccache wrapper and default-configuration handling, using the reported ~/.config/tuxmake/default settings and CCACHE_DIR behavior as the reproduction. Compare the selected cache directory with ccache 4.10.2 defaults on non-Windows and Windows systems. Done means tuxmake respects the effective ccache default instead of unconditionally using ~/.ccache.

Written by the indexing model from the issue text.