[AVX-512] Don't assume that the rounding mode argument to intrinsics is a constant. While clang will guarantee this, nothing in the backend will.
[AVX-512] Don't assume that the rounding mode argument to intrinsics is a constant. While clang will guarantee this, nothing in the backend will.

A non-constant value will now result in an isel error instead of just asserting or crashing due to a bad cast during lowering.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@290532 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm