runtime: Enable runtime to build on riscv64

Convert Rust arch to Go arch in Makefile, and add `riscv64-options.mk`
to provide definitions required for runtime to build on riscv64.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

src/runtime/Makefile

@@ -20,6 +20,9 @@ endif
 ifeq ($(ARCH),aarch64)
     override ARCH = arm64
 endif
+ifeq ($(ARCH),riscv64gc)
+    override ARCH = riscv64
+endif
 
 ARCH_DIR = arch
 ARCH_FILE_SUFFIX = -options.mk

src/runtime/arch/riscv64-options.mk

@@ -0,0 +1,13 @@
+# Copyright (c) 2024 Institute of Software, CAS.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+# riscv64 settings
+
+MACHINETYPE := virt
+KERNELPARAMS :=
+MACHINEACCELERATORS :=
+CPUFEATURES :=
+
+QEMUCMD := qemu-system-riscv64