[Libcxx] Add <source_location> header.
This requires the __builtin_source_location() builtin, as implemented
by GCC and Clang.
Fixes https://github.com/llvm/llvm-project/issues/56363
Differential Revision: https://reviews.llvm.org/D120634
NOKEYCHECK=True
GitOrigin-RevId: 73d94b19161355d06f20678d628555719eebbdcc
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index df0646e..bed5ee2 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -51,6 +51,7 @@
- P0339R6 - ``polymorphic_allocator<>`` as a vocabulary type
- P1169R4 - ``static operator()``
- P0415R1 - ``constexpr`` for ``std::complex``
+- P1208R6 - ``std::source_location``
Improvements and New Features
-----------------------------