[llvm] [CMake] Check objcopy support for LLVM_SPLIT_DWARF (PR #80500)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay requested changes to this pull request.

This check is not necessary. We requires GCC 7.4/8.1 (2018), which roughly corresponds to the binutils 2.30 era. The default `R_X86_64_REX_GOTPCRELX` clang emits requires something like binutils 2.25+.

https://github.com/llvm/llvm-project/pull/80500