[6.0] LLDB CMake: add option to link Swift content from Darwin toolchain

[edymtt]

Explanation: introduce a CMake option that allow LLDB binaries to link against Swift content in Darwin toolchains -- this is neeed by Apple internal configurations
Radar: rdar://127113448
Scope: CMake build logic that configure the build for LLDB binaries on Darwin platforms
Risk: low -- this behaviour is opt in
Testing:

• CI testing

Reviewed By: @JDevlieghere in #8647

[edymtt]

@swift-ci Please test

[edymtt]

@swift-ci test llvm

[edymtt]

LLVM Test jobs are failing when running lit tests

Failed Tests (5):
  Clang :: Driver/lanai-unknown-unknown.cpp
  Clang :: Driver/mipsel-nacl-defines.cpp
  Clang :: Driver/wasm32-unknown-unknown.cpp
  Clang :: Driver/wasm64-unknown-unknown.cpp
  Clang :: Driver/x86_64-nacl-defines.cpp

Cannot find readily any baseline reference (since most PRs targeting swift/release/6.0 focus on the Swift testing), so not considering them blocking.