Require Android SDK copy of CMake to build Vulkan on Android.

tools/build_shaderc.py

 #!/usr/bin/python
 
 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 
 """
 Script to build the shaderc library.
@@ skipping 55 matching lines @@
     os.makedirs(args.output_dir)
   except os.error:
     sys.exit('Error creating output dir ' + args.output_dir)
 
   try:
     build_type_arg='-DCMAKE_BUILD_TYPE=' + args.build_type
     cmake_cmd = ['cmake', '-G', generator,
                  '-DSPIRV_SKIP_EXECUTABLES=ON',
                  '-DSHADERC_ENABLE_SHARED_CRT=ON']
     if args.android_toolchain and args.android_toolchain.strip() :
-      cmake_cmd.append('-DCMAKE_TOOLCHAIN_FILE=' + args.src_dir +\
-                       '/third_party/android-cmake/android.toolchain.cmake')
+      cmake_cmd.append('-DCMAKE_TOOLCHAIN_FILE=' +\
+                       os.environ['ANDROID_SDK_ROOT'] +\
+                       '/cmake/android.toolchain.cmake')
       cmake_cmd.append('-DANDROID_TOOLCHAIN_NAME=standalone-clang')
       cmake_cmd.append('-DANDROID_STANDALONE_TOOLCHAIN=' +\
                        os.path.abspath(args.android_toolchain))
     cmake_cmd.extend([build_type_arg, args.src_dir])
     subprocess.check_call(cmake_cmd, cwd=args.output_dir)
   except subprocess.CalledProcessError as error:
     sys.exit('Error (ret code: {code}) calling "{cmd}" in {dir}'.format(
         code = error.returncode, cmd = error.cmd, dir = args.src_dir))
 
   try:
     subprocess.check_call(['cmake', '--build', args.output_dir, '--config',
         args.build_type], cwd=args.output_dir)
   except subprocess.CalledProcessError as error:
     sys.exit('Error (ret code: {code}) calling "{cmd}" in {dir}'.format(
         code = error.returncode, cmd = error.cmd, dir = args.src_dir))
 
 if __name__ == '__main__':
   main()