Merge "riscv64: stop reserving x18 for shadow call stack." am: 0ee012c2

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/2534260



Change-Id: I10fe38fe8da297f6b91b2d179ef7d3335efda047
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>