[3.x] GDNative: Fix Linux riscv warning about ignored `sysv_abi`

modules/gdnative/include/gdnative/gdnative.h

@@ -47,7 +47,7 @@ extern "C" {
 #endif
 
 #else // Linux/BSD/Web
-#if defined(__aarch64__) || defined(__arm__)
+#if defined(__aarch64__) || defined(__arm__) || defined(__riscv)
 #define GDCALLINGCONV
 #else
 #define GDCALLINGCONV __attribute__((sysv_abi))