[clang] [lldb] [llvm] [cmake][llvm] Limit the number of Xcode schemes created by default (PR #101243)

[Greg Clayton via llvm-commits]

clayborg wrote:

Can we add a cmake settings that allows users to add custom target names that will be added? I would love to use this for my common projects like:
```
-DCMAKE_LLVM_XCODE_TARGETS=lldb;llvm-dwarfdump;llvm-gsymutil;lld
```
And it would add those top level targets?

https://github.com/llvm/llvm-project/pull/101243