GN: More CrOS fixes

build/config/linux/BUILD.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.
 
 import("//build/config/linux/pkg_config.gni")
 import("//build/config/features.gni")
 import("//build/config/sysroot.gni")
 import("//build/config/ui.gni")
 import("//tools/generate_library_loader/generate_library_loader.gni")
 
 config("sdk") {
   if (sysroot != "") {
     cflags = [ "--sysroot=" + sysroot ]
     ldflags = [ "--sysroot=" + sysroot ]
 
     # Need to get some linker flags out of the sysroot.
     ldflags += [ exec_script("sysroot_ld_path.py",
         [ rebase_path("//build/linux/sysroot_ld_path.sh", root_build_dir),
           sysroot ],
         "value") ]
   }
+
+  # Set here because OS_CHROMEOS cannot be autodetected in build_config.h like
+  # OS_LINUX and the like.
+  if (is_chromeos) {
+    defines = [ "OS_CHROMEOS" ]
+  }
 }
 
 config("fontconfig") {
   libs = [ "fontconfig" ]
 }
 
 pkg_config("freetype2") {
   packages = [ "freetype2" ]
 }
 
@@ skipping 179 matching lines @@
     "pci_alloc",
     "pci_init",
     "pci_cleanup",
     "pci_scan_bus",
     "pci_fill_info",
     "pci_lookup_name",
   ]
 }
 
 # Looking for libspeechd? Use //third_party/speech-dispatcher