glsl: Add new atomic_uint built-in GLSL type.

v2: Fix GLSL version in which the type became available.  Add
    contains_atomic() convenience method.  Split off atomic counter
    comparison error checking to a separate patch that will handle all
    opaque types.  Include new ir_variable fields for atomic types.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/glsl/ir.cpp

@@ -1586,7 +1586,7 @@ ir_variable::ir_variable(const struct glsl_type *type, const char *name,
 			 ir_variable_mode mode)
    : max_array_access(0), max_ifc_array_access(NULL),
      read_only(false), centroid(false), invariant(false),
-     mode(mode), interpolation(INTERP_QUALIFIER_NONE)
+        mode(mode), interpolation(INTERP_QUALIFIER_NONE), atomic()
 {
    this->ir_type = ir_type_variable;
    this->type = type;