Add library for core memory routines.

The Rust compiler may emit calls to memcmp, memcpy, memmove and memset.
Usually these come from libc, but in bare-metal binaries they must be
provided somewhere. For now we only use bare-metal rust on aarch64, so
the Arm optimized-routines implementation seems like the best choice.

Bug: 223166344
Test: atest vmbase_example.integration_test
Change-Id: Id2439208160411dcde12be76fbaa22c30c24b81d