Add riscv64 support for base gn build am: f65f3c34c1

Original change: https://android-review.googlesource.com/c/platform/external/libchrome/+/2263700

Change-Id: Ib8463d5bc27b6f1043a1b995eea8b4d8f2094431
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>