[libFuzzer][Mac] Don't set use_cups true on Mac fuzzer builds.

Speculative fix for Mac libFuzzer build breakage.

Bug: 936849,831914
Change-Id: I7705682b79a9835ec014504f436af9cab83c01a3
Reviewed-on: https://chromium-review.googlesource.com/c/1494724
Auto-Submit: Jonathan Metzman <metzman@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Commit-Queue: Jonathan Metzman <metzman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636522}

printing/buildflags/buildflags.gni

@@ -16,9 +16,9 @@ declare_args() {
   # enable_basic_printing within the same declare_args() block.
   enable_print_preview = !is_android && !is_chromecast && !is_ios && !is_fuchsia
 
-  if (use_fuzzing_engine) {
+  if (use_fuzzing_engine && is_linux) {
     # For fuzzing, just restrict to chromeos and linux.
-    use_cups = is_linux
+    use_cups = true
   } else {
     use_cups = (is_desktop_linux || is_mac) && !is_chromecast && !is_fuchsia
   }