gpu/internal/shaders: generate shader variants

We're about to add Direct3D support, where shaders are written in
HLSL. Rather than write shaders twice (or more), convert them to
a GLSL variant understood by the glslcc cross-compiler and generate
the OpenGL ES 2.0 and HLSL variants. The HLSL is used by a future
change.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/shaders/intersect.vert

@@ -0,0 +1,22 @@
+#version 310 es
+  
+// SPDX-License-Identifier: Unlicense OR MIT
+
+precision highp float;
+
+layout(location = 0) in vec2 pos;
+layout(location = 1) in vec2 uv;
+
+layout(binding = 0) uniform Block {
+	vec2 scale;
+	vec2 offset;
+} uvparams;
+
+layout(location = 0) out vec2 vUV;
+
+void main() {
+  vec2 p = pos;
+  p.y = -p.y;
+  gl_Position = vec4(p, 0, 1);
+  vUV = uv*uvparams.scale + uvparams.offset;
+}