This is an alternative of D120395 and D120411.
Previously we use __bfloat16 as a typedef of unsigned short. The
name may give user an impression it is a brand new type to represent
BF16. So that they may use it in arithmetic operations and we don't have
a good way to block it.
To solve the problem, we introduced __bf16 to X86 psABI and landed the
support in Clang by D130964. Now we can solve the problem by switching
intrinsics to the new type.
What is this macro check used for?