rather than symlink the webm/vpx terms, use the same header as libvpx to
reference in-tree files
based on the discussion in:
https://codereview.chromium.org/12771026/
Change-Id: Ia3067ecddefaa7ee01550136e00f7b3f086d4af4
(cherry picked from commit d640614d54)
this would require a PRIuS or similar macro for proper platform
compatibility (Visual Studio for instance would be variants of %lu)
Change-Id: I1af530c7c358c91b845acde1d8c12ef46c2ef746