Linux: change gyp and add a shim header to build with system speex.

This will be useful for Linux distributions shipping Chromium.
The default setting is still to build with the bundled speex library.

More changes will be required (in src). This is the part in deps.

Review URL:

git-svn-id: 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
2 files changed