glsl/mesa: split gl_shader in two

There are two distinctly different uses of this struct. The first
is to store GL shader objects. The second is to store information
about a shader stage thats been linked.

The two uses actually share few fields and there is clearly confusion
about their use. For example the linked shaders map one to one with
a program so can simply be destroyed along with the program. However
previously we were calling reference counting on the linked shaders.

We were also creating linked shaders with a name even though it
is always 0 and called the driver version of the _mesa_new_shader()
function unnecessarily for GL shader objects.

Acked-by: Iago Toral Quiroga <itoral@igalia.com>

src/compiler/glsl/standalone.cpp

@@ -222,7 +222,7 @@ initialize_context(struct gl_context *ctx, gl_api api)
    ctx->Const.GenerateTemporaryNames = true;
    ctx->Const.MaxPatchVertices = 32;
 
-   ctx->Driver.NewShader = _mesa_new_shader;
+   ctx->Driver.NewShader = _mesa_new_linked_shader;
 }
 
 /* Returned string will have 'ctx' as its ralloc owner. */
@@ -412,7 +412,7 @@ standalone_compile_shader(const struct standalone_options *_options,
       }
 
       for (unsigned i = 0; i < MESA_SHADER_STAGES; i++) {
-         struct gl_shader *shader = whole_program->_LinkedShaders[i];
+         struct gl_linked_shader *shader = whole_program->_LinkedShaders[i];
 
          if (!shader)
             continue;