Bug#1112767: ccache: FTBFS with CMake 4

[Joel Rosdahl]

This is actually a regression in doctest 2.4.12. It has been worked around in
ccache upstream (not yet part of a released version):
https://github.com/ccache/ccache/commit/df7afbf241298a1090d08a89394be0f9b0ddc612

Joel