[compiler-rt] [compiler-rt][builtins] Switch to using __builtin_memcpy_inline (PR #69784)

[Saleem Abdulrasool via llvm-commits]

compnerd wrote:

@alexander-shaposhnikov, right.  Older clang will also not support this (it was added in 2020?). I think that we should double check with @rnk and @hansw about the need for building the builtins with MSVC support.

https://github.com/llvm/llvm-project/pull/69784