Have getarch downgrade the RISCV C910V target to GENERIC if compiler lacks vector support

Makefile.prebuild

@@ -72,7 +72,8 @@ endif
 
 getarch : getarch.c cpuid.S dummy $(CPUIDEMU)
 	avx512=$$(perl c_check - - $(CC) $(TARGET_FLAGS) $(CFLAGS) | grep NO_AVX512); \
-	$(HOSTCC) $(HOST_CFLAGS) $(EXFLAGS) $${avx512:+-D$${avx512}} -o $(@F) getarch.c cpuid.S $(CPUIDEMU)
+	rv64gv=$$(perl c_check - - $(CC) $(TARGET_FLAGS) $(CFLAGS) | grep NO_RV64GV); \
+	$(HOSTCC) $(HOST_CFLAGS) $(EXFLAGS) $${avx512:+-D$${avx512}} $${rv64gv:+-D$${rv64gv}} -o $(@F) getarch.c cpuid.S $(CPUIDEMU)
 
 getarch_2nd : getarch_2nd.c $(TARGET_CONF) dummy
 ifndef TARGET_CORE

getarch.c

@@ -1574,6 +1574,16 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #ifdef FORCE_C910V
 #define FORCE
 #define ARCHITECTURE    "RISCV64"
+#ifdef NO_RV64GV
+#define SUBARCHITECTURE "RISCV64_GENERIC"
+#define SUBDIRNAME      "riscv64"
+#define ARCHCONFIG   "-DRISCV64_GENERIC " \
+       "-DL1_DATA_SIZE=32768 -DL1_DATA_LINESIZE=32 " \
+       "-DL2_SIZE=1048576 -DL2_LINESIZE=32 " \
+       "-DDTB_DEFAULT_ENTRIES=128 -DDTB_SIZE=4096 -DL2_ASSOCIATIVE=4 "
+#define LIBNAME   "riscv64_generic"
+#define CORENAME  "RISCV64_GENERIC"
+#else
 #define SUBARCHITECTURE "C910V"
 #define SUBDIRNAME      "riscv64"
 #define ARCHCONFIG   "-DC910V " \
@@ -1582,6 +1592,7 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
        "-DDTB_DEFAULT_ENTRIES=128 -DDTB_SIZE=4096 -DL2_ASSOCIATIVE=4 "
 #define LIBNAME   "c910v"
 #define CORENAME  "C910V"
+#endif
 #else
 #endif