This patch implements Richard Sandiford's suggestion from
https://gcc.gnu.org/pipermail/gcc-patches/2023-May/618215.html
that wi::bswap (and a new wi::bitreverse) should be functions,
and ideally only accessors are member functions.  This patch
implements the first step, moving/refactoring wi::bswap.

This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32}
with no new failures.  Ok for mainline?


2023-05-28  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
        * fold-const-call.cc (fold_const_call_ss) <CFN_BUILT_IN_BSWAP*>:
        Update call to wi::bswap.
        * simplify-rtx.cc (simplify_const_unary_operation) <case BSWAP>:
        Update call to wi::bswap.
        * tree-ssa-ccp.cc (evaluate_stmt) <case BUILT_IN_BSWAP*>:
        Update calls to wi::bswap.

        * wide-int.cc (wide_int_storage::bswap): Remove/rename to...
        (wi::bswap_large): New function, with revised API.
        * wide-int.h (wi::bswap): New (template) function prototype.
        (wide_int_storage::bswap): Remove method.
        (sext_large, zext_large): Consistent indentation/line wrapping.
        (bswap_large): Prototype helper function containing implementation.
        (wi::bswap): New template wrapper around bswap_large.


Thanks,
Roger
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