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.
The kernel names for OpenMP are manually mangled and not ideal when we
report something to the user. We demangle them now, providing the
function and line number of the target region, together with the actual
kernel name.