SPV: Add auto location mapping of non-opaque non-block uniform variables.

Fix #1019.

Test/spv.noBuiltInLoc.vert

@@ -6,6 +6,10 @@ in  vec4 foo;
 layout(location = 0)
 out vec4 bar;
 
+uniform vec4 uv1;
+uniform float uv2;
+uniform vec3 uv3;
+
 void main()
 {
     bar = foo;