AMDGPU backend need to know whether floating point opcodes that support exception
flag gathering quiet and propagate signaling NaN inputs per IEEE754-2008, which is
conveyed by a function attribute "amdgpu-ieee". "amdgpu-ieee"="false" turns this off.
Without this function attribute backend assumes it is on for compute functions.
-mamdgpu-ieee and -mno-amdgpu-ieee are added to Clang to control this function attribute.
By default it is on. -mno-amdgpu-ieee requires -fno-honor-nans or equivalent.
Reviewed by: Matt Arsenault
Differential Revision: https://reviews.llvm.org/D77013
Yaxun (Sam) Liu