Fix gcc_version.gni to determine target GCC toolchain version for Chrome OS.

build/config/gcc/gcc_version.gni

 # 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.
 
 if (is_clang) {
   gcc_version = 0
 } else if (is_android) {
   import("//build/config/android/config.gni")
   if (is_android_webview_build) {
     gcc_version = 48
   } else {
     gcc_version = 49
   }
+} else if (is_chromeos) {

[jamesr, 2014/10/27 23:48:52]

what does being chromeos have to do with whether you are cross-compiling or not?
 I'm pretty sure the answer is nothing.  Did you mean to check if the host
toolchain == the current toolchain or something like that?

[Ben Chan, 2014/10/28 00:21:21]

After looking at common/build.gypi, it seems like the right fix is to always
check the target toolchain version as a fallback:

  gcc_version = exec_script("../../compiler_version.py", [ "target", "compiler"
], "value")

In common/build.gypi, most of the code uses gcc_version (instead of
host_gcc_version), which is based on `compiler_version target compiler`.

Do you agree?

+  gcc_version = exec_script("../../compiler_version.py", [ "target", "compiler" ], "value")
 } else {
-  gcc_version = exec_script("../../compiler_version.py", [ "host",  "compiler" ], "value")
+  gcc_version = exec_script("../../compiler_version.py", [ "host", "compiler" ], "value")
 }