[cmake] Make LLVM_ENABLE_LLD=ON work better on macOS

LLVM_LINKER_IS_LLD is now set with LLVM_ENABLE_LLD=ON (or LLVM_USER_LINKER=lld)
even on APPLE, and we pass -Wl,-order_file when LLVM_LINKER_IS_LLD on APPLE
too.

To make this straightforward, change the linker detection logic to go through
the compiler driver on APPLE like on the other platforms.

No intended behavior change if LLVM_ENABLE_LLD isn't set.

Differential Revision: https://reviews.llvm.org/D113021