A recent git commit (c8666cfb0be7c36be66f7f14aa013c8afa1a9d38) has broken the ability to compile the shader. It can be fixed by simply reverting the commit. (I don't follow why the change was made or where retval was supposed to be defined, perhaps it is coming in a future commit)
Fixed.
*** This bug has been marked as a duplicate of bug 15658 ***
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