Without this change I get link errors in firefox's libxul. It looks
like the linker expect a particular pattern for getting the GOT. This
patch changes webm to use the same pattern used by the compiler.
Cherry-picked from change: Iea8c2e134ad45c1dc7d221ff885a8429bfa4e057
Change-Id: I933aef1cdb5a976e6ad07618f631845de8a81ca4