top_srcdir is defined, not TOP_SRCDIR, making compilation fail.
Oops, sorry about that. Patch submitted to xorg-devel for review: http://lists.x.org/archives/xorg-devel/2010-December/017234.html
Pulled into git master: http://cgit.freedesktop.org/xorg/xserver/commit/?id=d5b0d58573ffb90ea70273cd013102168fd2a18a
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