[libcxx] Use generic builtins for popcount, clz and ctz (#86563)
Fixes #86556
Use `__builtin_popcountg` instead of `__buildin_popcount{l|ll}`
Use `__builtin_clzg instead` of `__buildin_clz{l|ll}`
Use `__builtin_ctzg instead` of `__builtin_ctz{l|ll}`
The generic variant of the builtins can be used to simplify some logic
with >= Clang 19 or >= GCC 14, where these generic variants are
available. As for backwards compatibility reasons, we can't completely
remove the old logic. Therefore, I left ToDo comments to address this,
as soon as support for pre Clang 19 as well as pre GCC 14 is dropped.
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Co-authored-by: Nick Desaulniers <nickdesaulniers@users.noreply.github.com>
GitOrigin-RevId: a6db20f2c39ecb5939890317068d5398c760746d
3 files changed
