riscv64: Implement "C" extension in assembler am: fddd6a4c78 am: 71321b13bb

Original change: https://android-review.googlesource.com/c/platform/art/+/2939939

Change-Id: Ib126c1ee780e5d71a899e031e71673cc1d03e92a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>