消除riscv编译警告 (#653)

base/hplatform.h

@@ -60,6 +60,8 @@
     #define ARCH_MIPS64
 #elif defined(__mips__)
     #define ARCH_MIPS
+#elif defined(__riscv)
+    #define ARCH_RISCV
 #else
     #warning "Untested hardware architecture!"
 #endif