x86-64: Save RDX and RCX before we use them as function parameters.

When the function call is indirect, these registers may be broken to load a function pointer.

x86_64-gen.c

@@ -582,6 +582,8 @@ void gfunc_call(int nb_args)
         vtop--;
     }
 
+    save_regs(0); /* save used temporary registers */
+
     /* Copy R10 and R11 into RDX and RCX, respectively */
     if (nb_reg_args > 2) {
         o(0xd2894c); /* mov %r10, %rdx */
@@ -590,8 +592,6 @@ void gfunc_call(int nb_args)
         }
     }
 
-    save_regs(0); /* save used temporary registers */
-
     func_sym = vtop->type.ref;
     func_call = FUNC_CALL(func_sym->r);
     oad(0xb8, nb_sse_args < 8 ? nb_sse_args : 8); /* mov nb_sse_args, %eax */