libc++: silence -Wnontrivial-memaccess warning with newer clang

Apply part of LLVM commit 71315698c91d0cda054b903da0594ca6f072c350 to
silence the -Wnontrivial-memaccess warning that is triggered any time
this function is instantiated by user code. This fixes another
buildworld failure with Clang HEAD.

Original commit message:
[clang] Warn about memset/memcpy to NonTriviallyCopyable types (#111434)
This implements a warning that's similar to what GCC does in that
context: both memcpy and memset require their first and second operand
to be trivially copyable, let's warn if that's not the case.

Reviewed by:	emaste, dim
MFC after:	1 week
Differential Revision: https://reviews.freebsd.org/D52534

1 files changed, 2 insertions, 1 deletions

diff --git a/contrib/llvm-project/libcxx/include/__memory/uninitialized_algorithms.h b/contrib/llvm-project/libcxx/include/__memory/uninitialized_algorithms.h
index 7475ef5cf85d..79cab80dcf73 100644
--- a/contrib/llvm-project/libcxx/include/__memory/uninitialized_algorithms.h
+++ b/contrib/llvm-project/libcxx/include/__memory/uninitialized_algorithms.h
@@ -642,7 +642,8 @@ __uninitialized_allocator_relocate(_Alloc& __alloc, _Tp* __first, _Tp* __last, _
     __guard.__complete();
     std::__allocator_destroy(__alloc, __first, __last);
   } else {
-    __builtin_memcpy(const_cast<__remove_const_t<_Tp>*>(__result), __first, sizeof(_Tp) * (__last - __first));
+    // Casting to void* to suppress clang complaining that this is technically UB.
+    __builtin_memcpy(static_cast<void*>(const_cast<__remove_const_t<_Tp>*>(__result)), __first, sizeof(_Tp) * (__last - __first));
   }
 }