use stock core_riscv.h for ch32 v2 v3

hw/bsp/ch32v20x/family.c

@@ -1,6 +1,18 @@
 #include <stdio.h>
+
+// https://github.com/openwch/ch32v307/pull/90
+// https://github.com/openwch/ch32v20x/pull/12
+#ifdef __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wstrict-prototypes"
+#endif
+
 #include "ch32v20x.h"
 
+#ifdef __GNUC__
+#pragma GCC diagnostic pop
+#endif
+
 #include "bsp/board_api.h"
 #include "board.h"