ccache: update to 4.2.1

ccache: update to 4.2.1

Update ccache to 4.2.1

While compiling on Gentoo, the ccache can not be compiled due to this
error:

/openwrt/build_dir/host/ccache-4.1/unittest/../src/third_party/doctest.h:4084:47: error: size of array 'altStackMem' is not an integral constant-expression
 4084 |         static char             altStackMem[4 * SIGSTKSZ];
      |                                               ^

This was fixed in ccache version 4.2.1 [1] by upgrading doctest [2].

[1] https://github.com/ccache/ccache/issues/825
[2] https://github.com/doctest/doctest/issues/473

Signed-off-by: DENG Qingfang <dqfext@gmail.com>
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com> [refresh patch]
(cherry picked from commit 3ebfd0078d6aa4848ee8f72640266bd0390f790a)
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
[improved commit message]