I built WiredTiger on a clean system using ninja.

mkdir build
cd build
cmake -G Ninja ../.
ninja

Then I ran ccache -s and noticed it had not been invoked.

Tracking this down, it is due to a minor typo introduced by WT-14975. These lines in CMakeLists.txt should not have commas in the set lines:

if(CCACHE)
    set(CMAKE_C_COMPILER_LAUNCHER, ${CCACHE})
    set(CMAKE_CXX_COMPILER_LAUNCHER, ${CCACHE})
    message(STATUS "Using ccache: ${CCACHE}")
endif()