Add AST expression builder functions for comparisons
Expose the comparison isl AST expressions to the user. This functionality
allows the user to combine multiple isl_ast_expr objects into a single one
representing the result of a logical comparison between them. It is
especially useful when we translate the resulting isl_ast_expr later into
another representation, e.g., LLVM-IR in Polly's runtime alias checks.
Signed-off-by: Johannes Doerfert <doerfert@cs.uni-saarland.de>
Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>