Hook up GN official build and branding.

build/config/compiler/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/sysroot.gni")
+
 # Base compiler configuration.
 config("compiler") {
   include_dirs = [ "//", root_gen_dir ]
   if (is_win) {
     cflags = [
       "/Gy",  # Enable function-level linking.
       "/GS",  # Enable buffer security checking.
       "/EHsc",  # Assume C functions can't throw exceptions and don't catch
                 # structured exceptions (only C++ ones).
     ]
@@ skipping 23 matching lines @@
     } else if (is_linux) {
       cflags += [ "-fstack-protector", "--param=ssp-buffer-size=4" ]
     }
 
     if (is_mac) {
       # Mac-specific compiler flags setup.
       # ----------------------------------
 
       # These flags are shared between the C compiler and linker.
       common_mac_flags = [
-        # Set which SDK to use.
-        # TODO(brettw) this needs to be configurable somehow.
-        "-isysroot", "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.7.sdk",
-
+        "-isysroot", sysroot,
         "-mmacosx-version-min=10.6",
       ]
 
       # CPU architecture.
       if (cpu_arch == "x64") {
         common_mac_flags += "-arch x86_64"
       } else if (cpu_arch == "x32") {
         common_mac_flags += "-arch i386"
       }
 
@@ skipping 54 matching lines @@
           # Experimentation found that using four linking threads
           # saved ~20% of link time.
           # https://groups.google.com/a/chromium.org/group/chromium-dev/browse_thread/thread/281527606915bb36
           # Only apply this to the target linker, since the host
           # linker might not be gold, but isn't used much anyway.
           "-Wl,--threads",
           "-Wl,--thread-count=4",
         ]
       }
 
+      if (sysroot != "") {
+        cflags += "--sysroot=" + sysroot
+        ldflags += "--sysroot=" + sysroot
+      }
+
       ldflags += [
         "-fPIC",
         "-pthread",
         "-Wl,-z,noexecstack",
         "-Wl,-z,now",
         "-Wl,-z,relro",
       ]
     }
 
     # Clang-specific compiler flags setup.
@@ skipping 269 matching lines @@
   } else {
     cflags = [ "-g1" ]
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }