switching checks handling

Author: devnexen

configure.ac

@@ -697,23 +697,17 @@ AC_CACHE_CHECK([for copy_file_range], ac_cv_copy_file_range,
 #define _GNU_SOURCE
 #endif
 #include <linux/version.h>
-#elif defined(__FreeBSD__)
-// TODO checks kernel version once this syscall is fixed on FreeBSD
-#include <sys/param.h>
-#include <sys/types.h>
-#endif
 #include <unistd.h>
 
 int main(void) {
 (void)copy_file_range(-1, 0, -1, 0, 0, 0);
-#if defined(__linux__)
 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,3,0)
-return 1;
+#error kernel too old;
 #else
 return 0;
 #endif
 #else
-return 1;
+#error unsupported by the platform
 #endif
 }
 ]])], [ac_cv_copy_file_range=yes], [ac_cv_copy_file_range=no])