I have taken the diff provided via this quite old bug report and added the CMake piece. Originally from FreeBSD/sparc64.
According to a developer at the FreeBSD project, FreeBSD's total compilation time increases by 2.6% when the host system is built against compiler-rt instead of libgcc. This is likely due to the fact that GCC has assembly-written versions of the division and modulo routines, while compiler-rt does not.
Is 2.6% still the case nowadays? It's hard to believe so much compile time is spent on division and modulo routines. We need evidence.
For these routines, ISTM the performance is not the critical part but maintainability is probably the most important metric. We should just use the portable C implementation.