Unimplemented x86 llvm intrinsic vcvtph2ps

[DGriffin91]

When compiling half I noticed two warnings for a missing x86 llvm intrinsic vcvtph2ps:

warning: unsupported x86 llvm intrinsic llvm.x86.vcvtph2ps.128; replacing with trap
warning: unsupported x86 llvm intrinsic llvm.x86.vcvtph2ps.256; replacing with trap

trap at Instance { def: Item(DefId(2:23219 ~ core[4322]::core_arch::x86::f16c::_mm_cvtps_ph)), args: [0_i32] } (_ZN4core9core_arch3x864f16c12_mm_cvtps_ph17heb7efe16215ebb1fE): llvm.x86.vcvtps2ph.128

Thanks for all your work on the cranelift backend for rust!

Edit: I guess this is might be related to https://github.com/rust-lang/rustc_codegen_cranelift/issues/1461