Revert Clang roll in r8596 + add memcheck suppression.

The roll seems to cause leaks on our Linux Memcheck bot.
Added a suppression needed for Trusty in order to run
memcheck similar to the bot (that runs Precise).
Leave all the other source code edits from r8596 in place.

See also http://chromegw/i/client.webrtc/builders/Linux%20Memcheck/builds/3343

TBR=pbos@webrtc.org
TESTED=Can no longer repro memcheck failure with this patch applied:
GYP_DEFINES="build_for_tool=memcheck" webrtc/build/gyp_webrtc
ninja -C out/Release libjingle_peerconnection_unittest
tools/valgrind-webrtc/webrtc_tests.sh --test libjingle_peerconnection_unittest --tool memcheck --target Release --build-dir out  --gtest_filter=WebRtcSessionTest.TestIncorrectMLinesInLocalAnswer

Review URL: https://webrtc-codereview.appspot.com/47419004

Cr-Commit-Position: refs/heads/master@{#8612}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8612 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed