* libm/common/s_lrint.c (lrint): Annotate shift operations with
possible shift amount ranges, and use SAFE_RIGHT_SHIFT to avoid
undefined behaviour.
* libm/common/s_llrint.c (llrint): Likewise.
* libm/common/s_lround.c (lround): Correct some comments on ranges.
* libm/common/s_llround.c (llround): Likewise.