st/mesa: fix setting of point_size_per_vertex in ES contexts
st/mesa: fix setting of point_size_per_vertex in ES contexts

GL ES 2.0+ does not have a GL_PROGRAM_POINT_SIZE enable, unlike desktop
GL. So we have to go and check the last pre-rasterizer stage to see
whether it outputs a point size or not.

This fixes a number of dEQP tests that use a geometry or tessellation
shader to emit points primitives.

Signed-off-by: Ilia Mirkin <bcbbb7aa705ec3a5fc5824c01a845186c3d62fca@alum.mit.edu>
Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>
Cc: "11.1 11.2" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler