Add yasm and ffmpeg into the build tree for linux.

third_party/ffmpeg/munge_config_optimizations.sh

+# Copyright (c) 2009 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 script munges the config.h to mark EBP unavailable so that the ffmpeg
+# library can be compiled as WITHOUT -fomit-frame-pointer allowing for
+# breakpad to work.
+#
+# Without this, building without -fomit-frame-pointer on ia32 will result in
+# the the inclusion of a number of inline assembly blocks that use too many
+# registers for its input/output operands.  This will cause gcc to barf with:
+#
+#   error: can't find a register in class ‘GENERAL_REGS’ while reloading ‘asm’
+#
+# This modification should only be required on ia32, and not x64.
+#
+# Note that HAVE_EBX_AVAILABLE is another flag available in config.h.  One would
+# think that setting this to 0 would allow for ffmpeg to be built with -fPIC.
+# However, not all the assembly blocks requiring 6 registers are excluded by
+# this flag.
+
+set -e
+
+sed -i.orig -e '
+/HAVE_EBP_AVAILABLE/ {
+c\
+#define HAVE_EBP_AVAILABLE 0
+}
+' \
+$1