[flang] Support late math lowering for intrinsics from the llvm table.

mathOperations should now support all intrinsics that are handled
by the llvmIntrinsics table + `tan` lowered as Math dialect operation +
f128 flavor of abs.

I am going to flip the default to late math lowering after this change,
but still keep the fallback via pgmath. This will allow getting rid
of the llvmIntrinsics table and continue populating
only the mathOperations table, otherwise, updating both tables
seems to be inconvenient.

Differential Revision: https://reviews.llvm.org/D130048