[committed] libstdc++: Add std::bit_cast for C++20 [PR 93121]

[Jonathan Wakely]

On 03/12/20 19:25 +0000, Jonathan Wakely wrote:
>Thanks to Jakub's addition of the built-in, we can add this to the
>library now. The compiler tests for the built-in are quite extensive,
>including verifying the constraints, so this only adds minimal tests to
>the library testsuite.
>
>This doesn't add a new _GLIBCXX_HAVE_BUILTIN_BIT_CAST because using
>__has_builtin(__builtin_bit_cast) works for GCC and versions of Clang
>that provide the built-in.
>
>libstdc++-v3/ChangeLog:
>
>	PR libstdc++/93121
>	* include/std/bit (__cpp_lib_bit_cast, bit_cast): Define.
>	* include/std/version (__cpp_lib_bit_cast): Define.
>	* testsuite/26_numerics/bit/bit.cast/bit_cast.cc: New test.
>	* testsuite/26_numerics/bit/bit.cast/version.cc: New test.

This fixes some typos in the new tests.

Tested x86_64-linux. Committed to trunk.


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