`std::launch::any` was a draft C++11 feature that was removed before the
final standard but it has remained in libc++ as an extension. This patch
marks it as deprecated and suggests using `std::launch::async |
std::launch::deferred` instead.
- Used `_LIBCPP_DEPRECATED_` to mark `std::launch::any` as deprecated
with an associated warning message recommending `std::launch::async |
std::launch::deferred` instead.
- Added a `.verify.cpp` test to validate the deprecation warning.
- Updated existing tests to avoid using the deprecated extension.
- Added note about deprecation in docs.
Fixes#173219
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Co-authored-by: Louis Dionne <ldionne.2@gmail.com>
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