Replacing hard-coded clang version by a common variable.

build/toolchain/toolchain.gni

 # Copyright 2015 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.
 
 # Toolchain-related configuration that may be needed outside the context of the
 # toolchain() rules themselves.
 
 declare_args() {
   # Enable Link Time Optimization in optimized builds (output programs run
   # faster, but linking is up to 5-20x slower).
   #
   # TODO(pcc): Remove this flag if/when LTO is enabled in official builds.
   allow_posix_link_time_opt = false
+
+  # Clang compiler version. Clang files are placed at version-dependent paths.
+  clang_version = "3.9.0"

[brettw, 2016/05/03 16:55:35]

Can this be an an is_clang condition so it's not defined in a non-clang build?

[aizatsky, 2016/05/03 17:21:24]

Done. Like this?

 }
 
 # Subdirectory within root_out_dir for shared library files.
 # TODO(agrieve): GYP sets this to "lib" for Linux & Android, but this won't work
 #     in GN until support for loadable_module() is added.
 #     See: https://codereview.chromium.org/1236503002/
 shlib_subdir = "."
 
 # Root out dir for shared library files.
 root_shlib_dir = root_out_dir
@@ skipping 32 matching lines @@
 stamp_description = "STAMP {{output}}"
 copy_description = "COPY {{source}} {{output}}"
 if (host_os == "win") {
   stamp_command = "$python_path gyp-win-tool stamp {{output}}"
   copy_command =
       "$python_path gyp-win-tool recursive-mirror {{source}} {{output}}"
 } else {
   stamp_command = "touch {{output}}"
   copy_command = "ln -f {{source}} {{output}} 2>/dev/null || (rm -rf {{output}} && cp -af {{source}} {{output}})"
 }