The intrinsic target prefix should match the target name
as it appears in the triple.
This is not yet complete, but gets most of the important ones.
llvm.AMDGPU.* intrinsics used by mesa and libclc are still handled
for compatability for now.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@258557 91177308-0d34-0410-b5e6-96231b3b80d8
