d3dcompiler: Unconditionally report special (pixel shader output) sysvals based on the semantic name.

That is, do not check that the shader is a pixel shader and that the signature
is an output signature. These semantic names can only be generated in such
conditions; using the name for any other stage is invalid.
Signed-off-by: Zebediah Figura <zfigura@codeweavers.com>
Signed-off-by: Matteo Bruni <mbruni@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>