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

[A. Jiang 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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frederick-vs-ja wrote:

[meta.unary.prop] and/or [tab:meta.unary.prop] will be suitable.

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