Remove -DPREFIX from win64 yasm_compile.gypi to fix ffmpeg linking

third_party/yasm/yasm_compile.gypi

 # Copyright (c) 2012 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 is an gyp include to use YASM for compiling assembly files.
 #
 # Files to be compiled with YASM should have an extension of .asm.
 #
 # There are two variables for this include:
 # yasm_flags : Pass additional flags into YASM.
@@ skipping 52 matching lines @@
       }],
       [ 'OS=="win" and target_arch=="ia32"', {
         'yasm_flags': [
           '-DPREFIX',
           '-fwin32',
           '-m', 'x86',
         ],
       }],
       [ 'OS=="win" and target_arch=="x64"', {
         'yasm_flags': [
-          '-DPREFIX',

[wolenetz, 2013/01/22 23:39:59]

try bots are failing update.  I'll sync my client, rebase the patch and submit
PS2 shortly.

           '-fx64',
           '-m', 'amd64',
         ],
       }],
 
       # Define output extension.
       ['OS=="win"', {
         'asm_obj_extension': 'obj',
       }, {
         'asm_obj_extension': 'o',
@@ skipping 23 matching lines @@
         '<(yasm_path)',
         '<@(yasm_flags)',
         '-o', '<(yasm_output_path)/<(RULE_INPUT_ROOT).<(asm_obj_extension)',
         '<(RULE_INPUT_PATH)',
       ],
       'process_outputs_as_sources': 1,
       'message': 'Compile assembly <(RULE_INPUT_PATH).',
     },
   ],  # rules
 }