libclc: Use elementwise exp for exp functions (#185626)
For amdgpu use the exp intrinisc. Really, this should be
the default generic implementation. But we're stuck in a
mess where essentially nothing works. All of the exp
intrinsics work for AMDGPU, but aren't really implemented
for spirv or nvptx. Ideally the intrinsic and/or libm call
would be the default implementation.
