Make GN Android build link executables

build/config/sysroot.gni

 # 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.
 
 # This header file defines the "sysroot" variable which is the absolute path

[cjhopman, 2014/05/12 18:37:17]

One sidenote here: Gyp has a problem where arguments to the compiler/linker that
include paths in the source tree need to be absolute because, unlike custom
actions/rules, the compiler and linker ninja targets are not run in the source
directory of the gyp file running them. This then means that, in gyp, there is
no way to actually calculate the path from the directory that compilation is
done to the source root-- that's because PRODUCT_DIR is a special variable that
isn't expanded until after all gyp processing (and in fact is expanded into
multiple different values).

We should make sure that gn does not require such arguments to use absolute
paths. This change already uses a relative path for finding the gold linker
where gyp requires an absolute path (well, gyp requires an absolute path to be
correct in all cases and can use <(PRODUCT_DIR)/../../ to be correct in the
common case of generating build files in out/Debug).

[brettw, 2014/05/12 21:00:09]

Yeah, GN always says root_build_dir is the current directory for all commands
executed, including actions and rules. I used to run actions in the same dir as
the source, but this got confusing so I decided to be consistent, even though in
some cases this makes actions more annoying to write.

 # of the sysroot. If no sysroot applies, the variable will be an empty string.
 
 if (is_android) {
   import("//build/config/android/config.gni")
   if (!is_android_webview_build) {
     if (cpu_arch == "x86") {
-      sysroot = "$android_ndk_root/platforms/android-14/arch-x86"
+      sysroot = rebase_path("$android_ndk_root/$x86_android_sysroot_subdir")
     } else if (cpu_arch == "arm") {
-      sysroot = "$android_ndk_root/platforms/android-14/arch-arm"
+      sysroot = rebase_path("$android_ndk_root/$arm_android_sysroot_subdir")
     } else if (cpu_arch == "mipsel") {
-      sysroot = "$android_ndk_root/platforms/android-14/arch-mips"
+      sysroot = rebase_path("$android_ndk_root/$mips_android_sysroot_subdir")
     } else {
       sysroot = ""
     }
   } else {
     sysroot = ""
   }
 } else if (is_linux && is_chrome_branded && is_official_build && !is_chromeos) {
   # For official builds, use the sysroot checked into the internal source repo
   # so that the builds work on older versions of Linux.
   if (cpu_arch == "x64") {
@@ skipping 14 matching lines @@
 } else if (is_mac) {
   import("//build/config/mac/mac_sdk.gni")
 
   sysroot = mac_sdk_path
 } else if (is_ios) {
   import("//build/config/ios/ios_sdk.gni")
   sysroot = ios_sdk_path
 } else {
   sysroot = ""
 }