report-fossil: add a parameter to discard stats

This adds a property to indicate that a statistic change makes all
other statistics uncomparable. This is quite useful on Intel where
shaders are compiled in different variants and a SIMD8 compute shader
cannot be compared to a SIMD16 variant. All that should be visible is
the change of SIMD width.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>