[Clang] Always use --no-undefined when linking AMDGPU images

AMDGPU uses ELF shared libraries to implement their executable device
images. One downside to this method is that it disables regular warnings
on undefined symbols. This is because shared libraries expect these to
be resolves by later loads. However, the GPU images do not support
dynamic linking so any undefined symbol is going to cause a runtime
error. This patch adds `--no-undefined` to the `ld.lld` invocation to guarantee
that undefined symbols are always caught as linking errors rather than
runtime errors.

Reviewed By: arsenm, MaskRay, #amdgpu

Differential Revision: https://reviews.llvm.org/D145941