Add SSE2 support for Windows.

The previous defines controlling SSE2 use assumed GCC. To fix this:
- Import a chunk of defines to typedefs.h from Chrome's build_config.h, primarily to get WEBRTC_ARCH_X86_FAMILY.
- Add a check derived from WebP to define WEBRTC_USE_SSE2.
- Modify cpu_features.cc to work with MSVC. This code is borrowed from chrome/src/base/cpu.cc.
- Change AEC defines to use WEBRTC_USE_SSE2.
- Remove disable_sse2 check from aec.gyp. This is handled by WEBRTC_USE_SSE2.

(Also remove a bit of unused code from aec_core.h)
Review URL: http://webrtc-codereview.appspot.com/95008

git-svn-id: http://webrtc.googlecode.com/svn/trunk@299 4adac7df-926f-26a2-2b94-8c16560cd09d
9 files changed