gn: Add asserts that libjpeg_turbo is not used on iOS.

build/secondary/third_party/libjpeg_turbo/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Do not use the targets in this file unless you need a certain libjpeg
 # implementation. Use the meta target //third_party:jpeg instead.
 
 import("//build/config/sanitizers/sanitizers.gni")
 if (current_cpu == "arm") {
   import("//build/config/arm.gni")
 }
 
+assert(!is_ios, "This is not used on iOS, don't drag it in unintentionally")
+
 if (current_cpu == "x86" || current_cpu == "x64") {
   import("//third_party/yasm/yasm_assemble.gni")
 
   yasm_assemble("simd_asm") {
     defines = []
 
     if (current_cpu == "x86") {
       sources = [
         "simd/jccolor-mmx.asm",
         "simd/jccolor-sse2.asm",
@@ skipping 190 matching lines @@
   # MemorySanitizer doesn't support assembly code, so keep it disabled in
   # MSan builds for now.
   if (is_msan) {
     sources += [ "jsimd_none.c" ]
   } else {
     deps = [
       ":simd",
     ]
   }
 }