Revert of Do not allow asan_symbolize.py to fall back to addr2line/atos.

tools/valgrind/asan/third_party/asan_symbolize.py

 #!/usr/bin/env python
 #===- lib/asan/scripts/asan_symbolize.py -----------------------------------===#
 #
 #                     The LLVM Compiler Infrastructure
 #
 # This file is distributed under the University of Illinois Open Source
 # License. See LICENSE.TXT for details.
 #
 #===------------------------------------------------------------------------===#
 import argparse
 import bisect
 import getopt
 import os
 import re
 import subprocess
 import sys
 
 symbolizers = {}
 DEBUG = False
 demangle = False
 binutils_prefix = None
 sysroot_path = None
 binary_name_filter = None
 fix_filename_patterns = None
 logfile = sys.stdin
-allow_system_symbolizer = True
 
 # FIXME: merge the code that calls fix_filename().
 def fix_filename(file_name):
   if fix_filename_patterns:
     for path_to_cut in fix_filename_patterns:
       file_name = re.sub('.*' + path_to_cut, '', file_name)
   file_name = re.sub('.*asan_[a-z_]*.cc:[0-9]*', '_asan_rtl_', file_name)
   file_name = re.sub('.*crtstuff.c:0', '???:0', file_name)
   return file_name
 
@@ skipping 349 matching lines @@
             self.system, guess_arch(addr), self.dsym_hints)
         self.llvm_symbolizers[binary] = self.last_llvm_symbolizer
     # Use the chain of symbolizers:
     # Breakpad symbolizer -> LLVM symbolizer -> addr2line/atos
     # (fall back to next symbolizer if the previous one fails).
     if not binary in symbolizers:
       symbolizers[binary] = ChainSymbolizer(
           [BreakpadSymbolizerFactory(binary), self.llvm_symbolizers[binary]])
     result = symbolizers[binary].symbolize(addr, binary, offset)
     if result is None:
-      if not allow_system_symbolizer:
-        raise Exception('Failed to launch or use llvm-symbolizer.')
       # Initialize system symbolizer only if other symbolizers failed.
       symbolizers[binary].append_symbolizer(
           SystemSymbolizerFactory(self.system, addr, binary))
       result = symbolizers[binary].symbolize(addr, binary, offset)
     # The system symbolizer must produce some result.
     assert result
     return result
 
   def get_symbolized_lines(self, symbolized_lines):
     if not symbolized_lines:
@@ skipping 65 matching lines @@
     binary_name_filter = sysroot_path_filter
     sysroot_path = args.s
   if args.c:
     binutils_prefix = args.c
   if args.logfile:
     logfile = args.logfile
   else:
     logfile = sys.stdin
   loop = SymbolizationLoop(binary_name_filter)
   loop.process_logfile()