Apply libc++ fix for compiling <type_traits> with clang 16

Merge commit 0e7971154ecb from llvm-project (by Christopher Di Bella):

[libcxx][NFC] utilises compiler builtins for unary transform type-traits

Depends on D116203

Reviewed By: #libc, philnik

Differential Revision: https://reviews.llvm.org/D131732

Clang 16 got new builtins that are equivalent to hand-written parts of
<type_traits>. When building world with the devel/llvm16 package
installed and CROSS_TOOLCHAIN=llvm16 set, this would lead to -Werror
warnings about those builtins being overridden.

Reported by: emaste
MFC after: 3 days