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

[Erich Keane via cfe-commits]

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@@ -1826,6 +1827,12 @@ The following type trait primitives are supported by Clang. Those traits marked
   functionally equivalent to copying the underlying bytes and then dropping the
   source object on the floor. This is true of trivial types and types which
   were made trivially relocatable via the ``clang::trivial_abi`` attribute.
+* ``__builtin_is_cpp_trivially_relocatable`` (C++): Returns true if and object
+  is trivially relocatable, as defined by the C++26 standard.
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erichkeane wrote:

TBH we probably should.  I asked for it because 'as defined by the C++26 standard' is pretty vague.

https://github.com/llvm/llvm-project/pull/127636