Remove Windows-related GN build configuration

build/config/BUILDCONFIG.gn

 # Copyright (c) 2013 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.
 
 if (target_os == "") {
   target_os = host_os
 }
 
 if (target_cpu == "") {
   if (target_os == "android") {
@@ skipping 135 matching lines @@
 # - is_mac is set only for desktop Mac. It is not set on iOS.
 # - is_posix is true for mac and any Unix-like system (basically everything
 #   except Windows).
 # - is_linux is true for desktop Linux and ChromeOS, but not Android (which is
 #   generally too different despite being based on the Linux kernel).
 #
 # Do not add more is_* variants here for random lesser-used Unix systems like
 # aix or one of the BSDs. If you need to check these, just check the
 # current_os value directly.
 
-if (current_os == "win") {
+if (current_os == "mac") {
   is_android = false
   is_chromeos = false
   is_fnl = false
-  is_ios = false
-  is_linux = false
-  is_mac = false
-  is_nacl = false
-  is_posix = false
-  is_win = true
-} else if (current_os == "mac") {
-  is_android = false
-  is_chromeos = false
-  is_fnl = false
   is_ios = false
   is_linux = false
   is_mac = true
   is_nacl = false
   is_posix = true
   is_win = false
 } else if (current_os == "android") {
   is_android = true
   is_chromeos = false
   is_fnl = false
@@ skipping 49 matching lines @@
 } else if (current_os == "fnl") {
   is_android = false
   is_chromeos = false
   is_fnl = true
   is_ios = false
   is_linux = true
   is_mac = false
   is_nacl = false
   is_posix = true
   is_win = false
+} else {
+  assert(false, "Unsupported operating system")
 }
 
 # =============================================================================
 # SOURCES FILTERS
 # =============================================================================
 #
 # These patterns filter out platform-specific files when assigning to the
 # sources variable. The magic variable |sources_assignment_filter| is applied
 # to each assignment or appending to the sources variable and matches are
 # automatcally removed.
@@ skipping 284 matching lines @@
 
 # ==============================================================================
 # TOOLCHAIN SETUP
 # ==============================================================================
 #
 # Here we set the default toolchain, as well as the variable host_toolchain
 # which will identify the toolchain corresponding to the local system when
 # doing cross-compiles. When not cross-compiling, this will be the same as the
 # default toolchain.
 
-if (is_win) {
-  # On windows we use the same toolchain for host and target by default.
-  if (is_clang) {
-    host_toolchain = "//build/toolchain/win:clang_$current_cpu"
-  } else {
-    host_toolchain = "//build/toolchain/win:$current_cpu"
-  }
-  set_default_toolchain("$host_toolchain")
-} else if (is_android) {
+if (is_android) {
   if (host_os == "linux") {
     # Use clang for the x86/64 Linux host builds.
     if (host_cpu == "x86" || host_cpu == "x64") {
       host_toolchain = "//build/toolchain/linux:clang_$host_cpu"
     } else {
       host_toolchain = "//build/toolchain/linux:$host_cpu"
     }
   } else if (host_os == "mac") {
     host_toolchain = "//build/toolchain/mac:clang_$host_cpu"
   } else {
@@ skipping 222 matching lines @@
       }
       if (defined(invoker.testonly)) {
         testonly = invoker.testonly
       }
       if (defined(invoker.visibility)) {
         visibility = invoker.visibility
       }
     }
   }
 }