Summary:
This is only really meaningful for the NVPTX target. Not all build
environments support host LTO and these are redundant tests, just clean
this up and make it run faster.
It appears that the RUNTIMES build prefers the x86-64-unknown-linux-gnu
triple notation for the host. This fixes runtime / test breakages when
compiler-rt is used as the CLANG_DEFAULT_RTLIB.