[InstCombine] Propagate FMF from select instead of fcmp (#141010)
Previously,
https://github.com/llvm/llvm-project/commit/3d6b53980ce4ee855484fc8ae6ac3f99c85e48c3
propagates FMF from fcmp to avoid performance regressions. With the help
of https://github.com/llvm/llvm-project/pull/139861,
https://github.com/llvm/llvm-project/pull/141015, and
https://github.com/llvm/llvm-project/pull/141914, we can still convert
SPF into fabs/minnum/maxnum intrinsics even if some flags are missing.
This patch propagates FMF from select to address the long-standing
issue.
Closes https://github.com/llvm/llvm-project/issues/140994.