ccache: updated to 4.8.1

Ccache 4.8.1

Bug fixes
Fixed an issue with the depend mode in combination with -- on the command line for Clang-based compilers.
Improved knowledge about MSVC debug flags so that non-debug /Z* options are once again supported.
Ccache no longer treats /Zi as unsupported for clang-cl.
Made the output format of ccache -k max_size parsable by ccache itself.

Build/CI improvements
Corrected ccache version in the macOS binary release.
Made it possible to build ccache with clang-cl on Windows.
Upgraded to doctest 2.4.11, thereby fixing a build issue on Solaris.

Documentation improvements
Added a remote file storage example with URL-encoded spaces.

(adam)