Does your piglit have the following commit?  Mesa was updated to follow the
spec, and the test was previously incorrect.

commit 63aef6af996d5ca37e9dee78e0392106848e2735
Author: Neil Roberts <neil@linux.intel.com>
Date:   Wed Nov 26 18:35:32 2014 +0000

    Don't test floats with the form ‘1f’

    There is nothing in the GLSL spec which says you can have a float
    literal without an exponent or a decimal point even if you add the ‘f’
    suffix. This patch replaces that literal with some other variations
    that should be accepted according to the spec.

    Reviewed-by: Matt Turner <mattst88 at gmail.com>