llvm: Pull RISC-V multi-lib YAML support patch

This commit pulls the LLVM patch that enables `multilib.yaml` support
for the RISC-V architecture.

Note that the hard-coded RISC-V multi-lib selection logic was
unconditionally used prior to this patch.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Author: stephanosio