[LLDB][CMake][NFC] Remove unused LLDB_LINKER_SUPPORTS_GROUPS variable

[jryans]

Summary

The LLDB_LINKER_SUPPORTS_GROUPS CMake variable was added back in 2019 as part
of https://reviews.llvm.org/D71306, but it appears to have been unused even
then. This removes the unused variable.

[JDevlieghere]

LGTM!

[bulbazord]

LGTM. I don't see any actual uses of this on llvm.org. If somebody needs it they can re-add it and add their use case or they can maintain a patch downstream.

lldb/cmake/modules/LLDBConfig.cmake

if(CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR)
   message(FATAL_ERROR
     "In-source builds are not allowed. CMake would overwrite the makefiles "
     "distributed with LLDB. Please create a directory and run cmake from "
     "there, passing the path to this source directory as the last argument. "
     "This process created the file `CMakeCache.txt' and the directory "
     "`CMakeFiles'. Please delete them.")
 endif()
 
-set(LLDB_LINKER_SUPPORTS_GROUPS OFF)
-if (LLVM_COMPILER_IS_GCC_COMPATIBLE AND NOT "${CMAKE_SYSTEM_NAME}" MATCHES "Darwin")
-  # The Darwin linker doesn't understand --start-group/--end-group.
-  set(LLDB_LINKER_SUPPORTS_GROUPS ON)
-endif()
-
 macro(add_optional_dependency variable description package found)
   cmake_parse_arguments(ARG
     "QUIET"
     "VERSION"
     ""
     ${ARGN})
 
   set(${variable} "Auto" CACHE STRING "${description} On, Off or Auto (default)")