[clang] [flang] [flang][driver] Don't use -whole-archive on Darwin (PR #75393)

[Andrzej Warzyński via cfe-commits]

banach-space wrote:

 > Unrelated to this PR, but may I ask how do you configure flang, to make it link without errors and without extra flags? I need to add `-L/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib`.

AFAIK, what you really want is this: `-isysroot $(xcrun --sdk-path)`. Today this happens to be:
*  `-L/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib`.

But there's no guarantee that this won't change in the future. Now, one should be able to "fix it" within one build of Clang with [DEFAULT_SYSROOT][(url](https://github.com/llvm/llvm-project/blob/c64334fb30f8a8087c218b6d7ec954ad47b33947/clang/CMakeLists.txt#L177-L178)). If that works for you - could you document in the Flang docs? 🙏🏻 

https://github.com/llvm/llvm-project/pull/75393