[flang] Support aint/anint for 80/128 bit in lowering

For aint/anint, LLVM conversion operations llvm.trunc and llvm.round
can support the edge case of aint(-0.) and anint(-0.). The output is -0.
and it is the same of `gfortran` and `classic flang`, while the output
of `ifort` is 0.. The `real(10)/real(16)` is not supported before.
Support it and remove the runtime functions for aint/anint.

For nint, `gfortran`, `ifort`, and LLVM Flang using llvm.lround have
different results when the magnitude of argument is more than the max of
result value range. So delay its support in lowering after more
investigations.

Reviewed By: vzakhari

Differential Revision: https://reviews.llvm.org/D130024