glsl: add language support for GL_ARM_shader_framebuffer_fetch_depth_stencil

This extension adds built-in variables gl_LastFragDepthARM and gl_LastFragStencilARM
which can be implemented almost the same as gl_LastFragData from color fetch extension.

Signed-off-by: Pavel Asyutchenko <sventeam@yandex.ru>
Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13979>

src/compiler/glsl/ir.h

@@ -612,6 +612,13 @@ public:
              this->name != this->name_storage;
    }
 
+   inline bool is_fb_fetch_color_output() const
+   {
+      return this->data.fb_fetch_output &&
+             this->data.location != FRAG_RESULT_DEPTH &&
+             this->data.location != FRAG_RESULT_STENCIL;
+   }
+
    /**
     * Enable emitting extension warnings for this variable
     */