glsl: add SYSTEM_VALUE_VERTEX_CNT

Used internally in freedreno/ir3 to calc stream-out position.  Seems
like a generic enough way to implement stream-out (using str instrs),
plus it avoids compiler warnings by sneaking in a non-enum value in
switch statements.

Signed-off-by: Rob Clark <robclark@freedesktop.org>

src/glsl/shader_enums.c

@@ -169,6 +169,7 @@ const char * gl_system_value_name(gl_system_value sysval)
      ENUM(SYSTEM_VALUE_TESS_LEVEL_INNER),
      ENUM(SYSTEM_VALUE_LOCAL_INVOCATION_ID),
      ENUM(SYSTEM_VALUE_WORK_GROUP_ID),
+     ENUM(SYSTEM_VALUE_VERTEX_CNT),
    };
    return NAME(sysval);
 }

src/glsl/shader_enums.h

@@ -412,6 +412,12 @@ typedef enum
    SYSTEM_VALUE_WORK_GROUP_ID,
    /*@}*/
 
+   /**
+    * Driver internal vertex-count, used (for example) for drivers to
+    * calculate stride for stream-out outputs.  Not externally visible.
+    */
+   SYSTEM_VALUE_VERTEX_CNT,
+
    SYSTEM_VALUE_MAX             /**< Number of values */
 } gl_system_value;