GN: Make sure we use clang when ASAN is specificed for ia32 Linux

tools/gn.py

 #!/usr/bin/env python
 # Copyright 2016 The Dart project 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 argparse
 import multiprocessing
 import os
 import subprocess
 import sys
@@ skipping 94 matching lines @@
   # should leave this set to 'develop', which causes the build to defer to
   # 'is_debug', 'is_release' and 'is_product'.
   gn_args['dart_runtime_mode'] = 'develop'
 
   # TODO(zra): Investigate using clang with these configurations.
   # Clang compiles tcmalloc's inline assembly for ia32 on Linux wrong, so we
   # don't use clang in that configuration.
   has_clang = (host_os != 'win'
                and args.os not in ['android']
                and not (gn_args['target_os'] == 'linux' and
-                        gn_args['host_cpu'] == 'x86')
+                        gn_args['host_cpu'] == 'x86' and
+                        not args.asan)  # Use clang for asan builds.
                and not gn_args['target_cpu'].startswith('arm')
                and not gn_args['target_cpu'].startswith('mips'))
   gn_args['is_clang'] = args.clang and has_clang
 
   gn_args['is_asan'] = args.asan and gn_args['is_clang']
 
   # Setup the user-defined sysroot.
   if gn_args['target_os'] == 'linux' and args.wheezy:
     gn_args['dart_use_wheezy_sysroot'] = True
   else:
@@ skipping 220 matching lines @@
       return 1
 
   endtime = time.time()
   if args.verbose:
     print ("GN Time: %.3f seconds" % (endtime - starttime))
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))