[Clang] Implement the core language parts of P2786 - Trivial relocation (#127636)

This adds

- The parsing of `trivially_relocatable_if_eligible`,
`replaceable_if_eligible` keywords
- `__builtin_trivially_relocate`, implemented in terms of memmove. In
the future this should
- Add the appropriate start/end lifetime markers that llvm does not have
(`start_lifetime_as`)
     - Add support for ptrauth when that's upstreamed

- the `__builtin_is_cpp_trivially_relocatable` and
`__builtin_is_replaceable` traits


Fixes #127609

1 files changed, 1 insertions, 0 deletions

diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index e083c1a..906b0fa 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -772,6 +772,7 @@ static void InitializeCPlusPlusFeatureTestMacros(const LangOptions &LangOpts,
   Builder.defineMacro("__cpp_pack_indexing", "202311L");
   Builder.defineMacro("__cpp_deleted_function", "202403L");
   Builder.defineMacro("__cpp_variadic_friend", "202403L");
+  // Builder.defineMacro("__cpp_trivial_relocatability", "202502L");
 
   if (LangOpts.Char8)
     Builder.defineMacro("__cpp_char8_t", "202207L");