nir/glsl: add nir_var_declared_implicitly enum

This will be used in the following patch.

Reviewed-by: Emma Anholt <emma@anholt.net>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22846>

src/compiler/glsl/glsl_to_nir.cpp

@@ -486,6 +486,9 @@ get_nir_how_declared(unsigned how_declared)
    if (how_declared == ir_var_hidden)
       return nir_var_hidden;
 
+   if (how_declared == ir_var_declared_implicitly)
+      return nir_var_declared_implicitly;
+
    return nir_var_declared_normally;
 }
 

src/compiler/nir/nir.h

@@ -430,6 +430,12 @@ typedef enum {
     */
    nir_var_declared_normally = 0,
 
+   /**
+    * Variable is an implicitly declared built-in that has not been explicitly
+    * re-declared by the shader.
+    */
+   nir_var_declared_implicitly,
+
    /**
     * Variable is implicitly generated by the compiler and should not be
     * visible via the API.