GLSL backend can't handle matrix-typed globals

[jimblandy]

When asked to produce GLSL from the following WGSL input, Naga declares the IR valid, but the GLSL back end produces the error "Non-struct type of a buffer":

@group(0)
@binding(0)
var<uniform> transform: mat4x4<f32>;

@stage(vertex)
fn main(
    @location(0) position: vec4<f32>,
) -> @builtin(position) vec4<f32> {
    return transform * position;
}

[jimblandy]

I'm working on this, but it turns out there's a lot about GLSL I don't know, so it's taking a bit longer than expected.