Fix content_unittests SandboxMacTest.BuiltinAvailable on pre-10.13.

Bug: 1114242, 1113952
Change-Id: Ie4ac3587177024f3c14bdca10515d5291063e1c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2342255Reviewed-by: Dominique Fauteux-Chapleau <domfc@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796043}

content/browser/sandbox_mac_unittest.mm

@@ -10,6 +10,7 @@
 #include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_file.h"
+#include "base/mac/mac_util.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/memory/ref_counted.h"
 #include "base/posix/eintr_wrapper.h"
@@ -265,11 +266,13 @@ MULTIPROCESS_TEST_MAIN(BuiltinAvailable) {
     return 10;
   }
 
+  if (base::mac::IsAtLeastOS10_13()) {
     if (__builtin_available(macOS 10.13, *)) {
       // Can't negate a __builtin_available condition. But success!
     } else {
       return 13;
     }
+  }
 
   return 0;
 }