add support for OpenBSD in ffmpeg

ffmpeg.gyp

 # Copyright (c) 2011 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.
 
 # There's a couple key GYP variables that control how FFmpeg is built:
 #   ffmpeg_branding
 #     Controls whether we build the Chromium or Google Chrome version of
 #     FFmpeg.  The Google Chrome version contains additional codecs.
 #     Typical values are Chromium, Chrome, ChromiumOS, and ChromeOS.
 #   use_system_ffmpeg
@@ skipping 33 matching lines @@
     # Allow overridding the selection of which FFmpeg binaries to copy via an
     # environment variable.  Affects the ffmpeg_binaries target.
 
     'conditions': [
       ['armv7==1 and arm_neon==1', {
         # Need a separate config for arm+neon vs arm
         'ffmpeg_config%': 'arm-neon',
       }, {
         'ffmpeg_config%': '<(target_arch)',
       }],
-      ['OS=="mac" or OS=="win"', {
+      ['OS=="mac" or OS=="win" or OS=="openbsd"', {
         'os_config%': '<(OS)',
       }, {  # all other Unix OS's use the linux config
         'os_config%': 'linux',
       }],
       ['chromeos==1', {
         'ffmpeg_branding%': '<(branding)OS',
       }, {  # otherwise, assume Chrome/Chromium.
         'ffmpeg_branding%': '<(branding)',
       }],
     ],
@@ skipping 156 matching lines @@
                       '-m', 'amd64',
                       '-DPIC',
                       # The next two lines are needed to enable AVX assembly.
                       '-Iconfig/<(ffmpeg_branding)/<(os_config)/<(ffmpeg_config)',
                       '-Pconfig.asm',
                     ],
                   }],
                 ],
               },
             }],  # OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris"
+            ['OS=="openbsd"', {
+              # OpenBSD's gcc (4.2.1) does not support this flag
+              'cflags!': [
+                '-fno-signed-zeros',
+              ],
+            }],
             ['OS=="mac"', {
               'conditions': [
                 ['mac_breakpad==1', {
                   'variables': {
                     # A real .dSYM is needed for dump_syms to operate on.
                     'mac_real_dsym': 1,
                   },
                 }],
               ],
               'link_settings': {
@@ skipping 286 matching lines @@
       ],  # conditions
     },
   ],  # targets
 }
 
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