CMP0155: ignore scanning for sources if no scanner is available
requested to merge ben.boeckel/cmake:cxxmodules-cmp0155-graceful-fallback-without-scanner into master
This allows for a more graceful transition for projects using C++20
without scanner support (e.g., Clang 15 or GCC 13). While newer
compilers will (needlessly) scan, it allows C++20-using projects to use
older compilers without having to set CMAKE_CXX_SCAN_FOR_MODULES to
support newer CMake minimum versions.
Fixes: #25357 (closed)
Backport: release
Edited by Brad King