26 Match and Simplify

The GIMPLE and GENERIC pattern matching project match-and-simplify tries to address several issues.

1. unify expression simplifications currently spread and duplicated over separate files like fold-const.c, gimple-fold.c and builtins.c
2. allow for a cheap way to implement building and simplifying non-trivial GIMPLE expressions, avoiding the need to go through building and simplifying GENERIC via fold_buildN and then gimplifying via force_gimple_operand

To address these the project introduces a simple domain specific language to write expression simplifications from which code targeting GIMPLE and GENERIC is auto-generated. The GENERIC variant follows the fold_buildN API while for the GIMPLE variant and to address 2) new APIs are introduced.