Detect CCache for cross compilation even if it's not explicit in cross-file

I'm doing some cross-compilation and I found out Meson does not find ccache when cross compiling.

[Here](https://github.com/mesonbuild/meson/issues/1392) it's said Ccache should be explicitly added in the cross-compilation file, but I think it shouldn't. Meson should first read the cross file, then search for ccache as usual.

Start by reproducing the cross-compilation case described in the issue and inspect how Meson reads the cross file before searching for ccache. Done means ccache is detected during cross compilation without being explicitly listed in the cross file, with coverage for that behavior if the relevant tests are found.

Written by the indexing model from the issue text.