glsl: add IR fields for transform feedback layout qualifiers

Adds xfb_buffer/stride fields and adds comment to offset field
which is reused for xfb_offset.

Reviewed-by: Dave Airlie <airlied@redhat.com>

src/compiler/glsl/ir.h

@@ -726,6 +726,21 @@ public:
        */
       unsigned is_xfb_only:1;
 
+      /**
+       * Was a transfor feedback buffer set in the shader?
+       */
+      unsigned explicit_xfb_buffer:1;
+
+      /**
+       * Was a transfor feedback offset set in the shader?
+       */
+      unsigned explicit_xfb_offset:1;
+
+      /**
+       * Was a transfor feedback stride set in the shader?
+       */
+      unsigned explicit_xfb_stride:1;
+
       /**
        * If non-zero, then this variable may be packed along with other variables
        * into a single varying slot, so this offset should be applied when
@@ -861,7 +876,7 @@ public:
       unsigned stream;
 
       /**
-       * Atomic or block member offset.
+       * Atomic, transform feedback or block member offset.
        */
       unsigned offset;
 
@@ -872,6 +887,16 @@ public:
        */
       unsigned max_array_access;
 
+      /**
+       * Transform feedback buffer.
+       */
+      unsigned xfb_buffer;
+
+      /**
+       * Transform feedback stride.
+       */
+      unsigned xfb_stride;
+
       /**
        * Allow (only) ir_variable direct access private members.
        */