piglit/tests/glslparsertest/shaders/preprocess1.frag gets pass with mesa:
It seems the test case expects to get fail with macro t2 redefinition (and the redefinition is not "effectively the same").
// tests for macro redifinition (t2) and the #if and #else nestings.
// takes care of elif also.
#define t1 (1+2)
#define t2 2
#define t2 3
Author: Carl Worth <email@example.com>
Date: Tue Aug 17 23:20:58 2010 -0700
glcpp: Add support for "redefined macro" error.
Carefully avoiding printing any error when the new definition matches
the existing definition.
This fixes the recently-added 088-redefine-macro-legitimate.c and
089-redefine-macro-error.c tests as well as glsparsertest/preprocess1
on Jun 27, 2016 at 13:01:57.
(provided by the Example extension).