[cuda] Ignore "TLS unsupported by target" errors for host variables during device compilation.

During device-side CUDA compilation clang currently complains about
all TLS variables, regardless of whether they are host or
device.

This patch suppresses "TLS unsupported" errors for host variables
during device compilation and for device variables during host
compilation.

Differential Revision: http://reviews.llvm.org/D9269