[libc++] [C++20] [P0415] Constexpr for std::complex.
This patch adds constexpr to <complex> header: operators, member operators, and member functions (real, imag, norm, conj).
https://eel.is/c++draft/complex.numbers
https://wg21.link/p0415
Reviewed By: ldionne, #libc
Spies: philnik, danilaml, Quuxplusone, wmaxey, arichardson, libcxx-commits
Differential Revision: https://reviews.llvm.org/D79555
NOKEYCHECK=True
GitOrigin-RevId: 7223bcf04c4ce3c1585df9408c6a6663cc8364ea
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index ba710c0..df0646e 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -50,6 +50,7 @@
- P0600R1 - ``nodiscard`` in the library
- P0339R6 - ``polymorphic_allocator<>`` as a vocabulary type
- P1169R4 - ``static operator()``
+- P0415R1 - ``constexpr`` for ``std::complex``
Improvements and New Features
-----------------------------