gn: Fix more build issues on Win

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.
 
 if (cpu_arch == "arm") {
   import("//build/config/arm.gni")
 }
@@ skipping 95 matching lines @@
 }
 
 }
 
 source_set("simd") {
   if (cpu_arch == "x86") {
     deps = [ ":simd_asm" ]
     sources = [
       "simd/jsimd_i386.c",
     ]
+    if (is_win) {
+      cflags = [ "/wd4245" ]
+    }
   } else if (cpu_arch == "x64") {
     deps = [ ":simd_asm" ]
     sources = [
       "simd/jsimd_x86_64.c",
     ]
   } else if (cpu_arch == "arm" && arm_version >= 7 &&
              (arm_use_neon || arm_optionally_use_neon)) {
     sources = [
       "simd/jsimd_arm.c",
       "simd/jsimd_arm_neon.S",
@@ skipping 81 matching lines @@
   # MSan builds for now.
   # TODO: Enable on Linux when .asm files are recognized.
   if (is_msan || is_linux) {
     sources += [ "jsimd_none.c" ]
   } else {
     deps = [ ":simd" ]
   }
 
   # TODO(GYP): Compile the .asm files with YASM as GYP does.
 }