glsl: don't always reject shaders with mismatching ifc blocks

glsl: don't always reject shaders with mismatching ifc blocks

Since we store some member qualifiers in the interface type
we need to be more careful about rejecting shaders just because
the pointer doesn't match. Its perfectly valid for some qualifiers
such as precision to not match across shader interfaces.

Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>