add cmake rvv support (#10411)

ggml/src/ggml-cpu/CMakeLists.txt

@@ -244,6 +244,11 @@ elseif (${CMAKE_SYSTEM_PROCESSOR} MATCHES "loongarch64")
     if (GGML_LSX)
         list(APPEND ARCH_FLAGS -mlsx)
     endif()
+elseif (${CMAKE_SYSTEM_PROCESSOR} MATCHES "riscv64")
+    message(STATUS "RISC-V detected")
+    if (GGML_RVV)
+        list(APPEND ARCH_FLAGS -march=rv64gcv -mabi=lp64d)
+    endif()
 else()
     message(STATUS "Unknown architecture")
 endif()