std::bit_cast needs include of

Summary

A use of std::bit_cast<> was added in 8b9dbcda but the required <bit> header was not included

This generates the the following error when building eigen3 within Chromium.

In file included from ../../third_party/eigen3/src/Eigen/Core:184: ../../third_party/eigen3/src/Eigen/src/Core/NumTraits.h:103:15: error: declaration of 'bit_cast' must be imported from module 'std.bit.bit_cast' before it is required 103 | return std::bit_cast(src); | ^ gen/third_party/libc++/src/include/__bit/bit_cast.h:36:55: note: declaration here is not visible 36 | nodiscard _LIBCPP_HIDE_FROM_ABI constexpr _ToType bit_cast(const _FromType& __from) noexcept { | ^ 1 error generated.

Environment

• Operating System : Linux
• Architecture : x64
• Eigen Version : HEAD
• Compiler Version : clang HEAD